Buenos Aires, capital of Argentina, has an extensive amount of underground city in its Subte (the oldest subway system in South America). Most stations have small shops, bars and kiosks, while main hubs interconnect through underground pedestrian walkways with railroad stations, governmental buildings or shopping centres. Some have additional mall-like mezzanine levels, with the Centro Obelisk of Buenos Aires area (3 lines, 4 underground levels), Estacion Retiro, Estacion Constitucion, Estacion Once and Federico Lacroze railway station being the most important ones.
Sydney has a series of underground shopping malls around one of the city's underground stations Town Hall. The tunnels run south to the George Street cinema district, west under the town hall, and north to Pitt Street Mall through the Queen Victoria Building. The northern branch links Queen Victoria Building with Galleries Victoria, Sydney Central Plaza (which in turn links internally above ground to Westfield Centrepoint, Imperial Arcade, Skygarden, Glasshouse, and the MLC Centre). The linked centres run for over 3 km. In 2005 Westfield corporation submitted a development application to link Sydney Central Plaza underground with 3 other properties on Pitt Street Mall and extend the tunnel network by a further 500m.
Edmonton has a small system of tunnels and above-ground skyways called the Pedway connecting buildings and LRT stations of the downtown core.
Halifax (Downtown Halifax Link) where no point is more than 10 minutes casual walking distance from any other one.
Montreal Underground city, or la ville souterraine in French, is the largest underground network in the world. Its 32 km of tunnel cover more than 41 city blocks (about 12 km²). Access through the RÉSO can be made to apartment buildings, hotels, offices, banks, and universities, as well as public spaces like retail shops and malls, concert halls, cinemas, the Bell Centre hockey arena, museums, seven metro stations, two train stations (Lucien-L'Allier and Gare Centrale), a bus terminal (Réseau de transport de Longueuil and other transit authorities), and other areas. It connects 80% of office space and 35% of commercial space in downtown Montreal.
The network began as a connection between Place Ville Marie, the Queen Elizabeth Hotel and the Gare Centrale.
More than 2,000 shops and 40 cinemas line the passageways. Tourists often visit various attractions in the underground city, which is used by an average of half a million Montrealers per day.
Eight metro stations link to smaller networks that are not yet part of the central network, such as Berri UQAM in the eastern part of downtown, and Pie-IX which links venues from the 1976 Summer Olympics. Additionally, other underground networks exist that are not part of the metro system, such as the La Cité housing and retail complex.
St. John's, Newfoundland and Labrador - At the main campus of Memorial University of Newfoundland are the MUNnels, a tunnel system, in which all the main buildings are connected, though there are also some elevated walkways.
Toronto (PATH), comprises 27 km of walkways and 1,200 shops. It links many important buildings and attractions downtown to six TTC subway stations. PATH accommodates 100,000 pedestrians daily, and PATH businesses host the world's largest underground sidewalk sale once annually.
The PATH network in Toronto is the largest underground shopping complex in the world with 371,600 square metres (4,000,000 sq ft).
Toronto also has a separate, smaller "underground city" connecting several building complexes and two subway stations on Bloor Street.
Vancouver has two shopping malls, Pacific Centre and Vancouver Centre, that are interconnected and extend over 3 city blocks, containing more than 200 stores that weaves above and below ground level. These malls are also connected to Granville SkyTrain Station and Vancouver City Centre Station on the Canada Line.
Winnipeg has a smaller (mainly commercial office) area located underground in the downtown core below Portage and Main. Several of the downtown office towers have subterranean entrances to the complex allowing employees and visitors to bypass the downtown traffic and avoid the cold winter temperatures Winnipeg regularly experiences. The system links with the skyway system known as the Winnipeg Walkway. Also the University of Manitoba has underground tunnels for the students to travel building to building.
Santiago has an extensive amount of underground city in its "Metro" subway system. All stations have a typical mezzanine level, but the Metro has this level full of shops and kiosks of all kinds, most stations have an additional mall-like level between the street and the mezzanine levels with the trains running at the 3 level down.
Beijing built an extensive tunnel network called the Underground City (simplified Chinese: 地下城; traditional Chinese: 地下城; pinyin: Dìxià Chéng) during the Sino-Soviet conflict, supposedly covering 85 km², falling into disuse in the 1970s. Now recently opened to the public and tourists. There are rumors saying it was used by the army during the Tiananmen incident. A tourist report describes the facility. As of 1st July 2009, all "official" remaining entrances appear to be closed.
Shanghai also has a few underground networks, most notably at the People's Square metro station, wherein the line 2 station has a second mezzanine full of shops and line 1 is connected to a large underground shopping gallery at its south end. Shanghai Science Museum stop on line 2 also has a large underground shopping area, known for its imitation goods. Huangpi Road South and Xujiahui stations are also directly connected to shopping centers, and the Lujiazui station is connected to the Bank of China tower.
Qingdao has two small underground shopping areas, one at the head of the Zhanqiao (pier) and one west of the Qingdao guest house.
Helsinki covering central railway station area, three subway stations (Rautatientori, Kamppi and Kaisaniemi) and shopping malls. The Kamppi metro station is integrated with the Kamppi Center (55,500 m²) long-distance bus terminal, freight depot and internal parking area, all underground. It also features a six-storey shopping complex and a central bus terminal for local buses. The underground network has connections to the nearby Forum shopping centre and Sokos and Stockmann department stores.
Two other subway stations in Helsinki have similar, although smaller undergrounds; Hakaniemi and Sörnäinen.
Paris The Forum des Halles, is a partially underground multiple story commercial and shopping center, opened in 1979. The building is connected to the underground station Chatelet-Les-Halles, central hub of Paris's express metro system, the RER. There was also more than 300 km of a network of catacombs, started as limestone quarries and later for burials, also used as safe passageways in times of revolution.
Frankfurt am Main Underground shopping malls, called 'B-Ebene' in Frankfurt, of considerable size are found at Hauptbahnhof (central station) and Hauptwache.
Hamburg The Jungfernstieg and Rathaus subway stations and several entrances are connected by pedestrian tunnels. Some of them contain shops. There is also a direct access to the Europapassage shopping mall.
Stuttgart There is a large underground shopping mall (Klettpassage) connecting the Hauptbahnhof (central station) with the main shopping street, the Königstraße.
Berlin Several buildings on the east side of Friedrichstraße, from Quartier 205 (Friedrichstraße 70) northwards up to Galerie Lafayette are connected to each other. Businesses are on both sides of that underground street so that it appears to be inside a building all the time, even when it crosses Taubenstraße underground. There are also various underground remnants of the planned city of Germania dating from the 1930s, including an extensive U-Bahn station.
Athens Athens has a small underground network, in Omonia square subway station there are some small newspapers kiosks, Syntagma, Evaggelismos and Akropolis stations antiquities are displays with the subway stations operating as open museums.
Hong Kong - Many MTR stations in Hong Kong form extended underground networks connecting to buildings and major shopping malls in the neighbouring areas. The stations themselves house a number of retail shops. Notable examples are the Central - Hong Kong stations, the Tsim Sha Tsui - East Tsim Sha Tsui stations.
Kish - An underground city by the name of Hidden Pearl was constructed which consists of roads interlinked 20 meters under the ground. Shops and restaurants are planned to be built.
Ancient Rome had a network of catacombs, ancient Jewish and Christian underground burial places near the city.
Naples has many chambers and tunnels beneath the city, including channels and reservoirs for water, and catacombs.
The top five largest underground "cities" (地下街, chikagai) in Japan are all shopping districts:
Crysta Nagahori in Chūō-ku, Osaka — 81,765 m²
Yaesu Chikagai in Chūō, Tokyo — 73,253 m²
Kawasaki Azalea in Kawasaki-ku, Kawasaki — 56,704 m²
Central Park Chikagai in Naka-ku, Nagoya — 56,370 m²
Diamor Osaka in Kita-ku, Osaka — 42,977 m²
Osaka has enormous underground networks in the Umeda, Namba, and Shinsaibashi districts, in which Umeda alone includes over 1,200 retail stores and restaurants, subway and intercity rail stations.
Tokyo's subway lines are owned by Eidan (9 lines) and Toei (4 lines), mostly within the 23 special wards. Near the center of the city, connecting passages between stations that span a few blocks exist for commuters. Stations such as Shinjuku and Shibuya have underground shopping malls. Tokyo's network of tunnels is seen as one of the many megalopolis features of the city.
Guanajuato: the city was built over old silver mines, some of which are used as roads. the Mexico DF metro system has many underground pedestrian walkways interconnecting stations.
Pakistan's largest cities of Karachi and Lahore are megapolis and have proposed for a future construction for underground metro systems.
Moscow: "Okhotnyi Ryad" (Охотный Ряд) four-level underground shopping mall — 29,000 m², linked to Metro station of same name.
Moscow Metro 2 a purported secret underground metro system in Moscow built supposedly during (or from) the time of Stalin.
Extensive underground networks exist around most major stations of the Mass Rapid Transit, such as the one at the Raffles Place MRT Station with direct underground connections to 19 buildings in the busy Raffles Place area. Expanding the network further, is the first phase of a new subterranean network linking the station to the up-coming One Raffles Quay development and with provisions to extend it into the Marina Bay new downtown extension for a complex underground pedestrian nework across the entire downtown area.
The CityLink Mall offers over 60,000 square feet of underground retail space and connects the City Hall MRT Station with Suntec City, the Esplanade - Theatres on the Bay, and other developments in the Marina Centre area. It will also be linked to the Esplanade MRT Station when the Circle MRT Line is completed by 2010.
The Orchard Road shopping belt is connected by underground linkways often with commercial space, particularly around the three MRT stations serving the district, namely Orchard , Somerset , and Dhoby Ghaut . Plans are in place to link all buildings along the road into a continuous underground network on both sides of the over four kilometre long road.
In Barcelona: There's an abandoned underground mall near Plaça de Catalunya called Avinguda de la Llum, closed since 1990, which had originally been part of a more ambitious project to build an underground city underneath the centre of Barcelona. Also, some Metro stations or connecting lines in the same station are connected by underground passages over a block in length.
In Madrid
In Bilbao, Valencia, Sevilla and Palma de Mallorca
Legend has that the many caves and tunnels under the old part of Toledo were connected and were used by occultists.
Geneva contains a large underground shopping centre which also acts to connect separate sections of surface shops.
St. Gallen's main hospital utilizes several underground tunnels to connect the various buildings, helicopter pad, pharmacies and storage facilities.
Zürich Hauptbahnhof in Zürich has an underground RailCity shopping mall with full access to the station platforms.
An underground mall in Taipei connecting two Taipei MRT stations.Taipei - underground streets connecting two or more metro stations. In addition, there is a large underground shopping mall near the main train station.
See also: Taipei Underground Market
The Bangkok Metro in Thailand is steadily expanding its network of underground MRT malls between far flung exits. Unlike most cities, they mainly serve to escape the heat and as street crossings.
This section may require cleanup to meet Wikipedia's quality standards. Please improve this section if you can. (July 2007)
Cappadocia contains several historical underground cities carved out of unusual geological formations formed via the eruptions of ancient volcanoes. The cities were initially inhabited by the Hittites, then later by early Christians as hiding places (see ). They are now archeological and tourist sites, but are not generally occupied (see Kaymaklı Underground City and Derinkuyu). The latest large underground city was discovered in 2007 in Gaziemir, Güzelyurt. This city was a stopover on the Silk Road, allowing travelers and their camels to rest in safety underground, in a 'fortress' equivalent to a modern hotel.
Kiyv - An underground concourse extends underneath Khreschatyk Street from Maidan Nezalezhnosti to Ploscha L'va Tolstoho. The concourse connects to the Kyiv Metro and to the Globe shopping mall beneath Maidan Nezalezhnosti.
In London's redeveloped docklands Canary Wharf tube station, adjacent office towers and shopping malls are connected underground. It is also possible to access two stations of the Docklands Light Railway without going outside.
Dover contains a series of interconnecting tunnels, that honeycomb both sides of the Dover Valley, carved into the chalk cliffs. These date from Ancient times at Dover Castle through to Napoleonic, Second and Cold War installations. The Dover Castle complex is the larger, going at least six levels deep and includes a hospital, troops quarters, offices and storage and channel view points. The southern tunnels are mixed between Napoleonic War-era defences (see Dover Western Heights ) and Second World War-era defences, with some seafront air raid shelters still used for shop storage today. Many have fallen into disrepair and are now closed to the public, but many are still open : See this or this.
There are extensive rooms, tunnels and chambers beneath some areas of Edinburgh's old Town.
Nevill Street, in Southport, Merseyside, has the remainders of an underground shopping street, which can now only be accessed from the cellars of buildings on the current street, which was raised by one storey from the original level. One end of the underground street ended at the Marine Lake, close to the pier entrance. 
The Williamson's tunnels in Liverpool, Merseyside, included the site of an 'underground house' complete with windows (concealed by work for public opening) and an extant and partially excavated 'banqueting hall'.
Albany, New York - Empire State Plaza in Albany, New York features an underground city which contains banks, a YMCA, restaurants, several food courts, retailers, a police station, a bus station, and a visitor's Center. The Plaza connects several government buildings to the Egg (a state-owned theater), the New York State Museum, The New York State Library, The Corning Tower (the tallest building between New York City and Toronto), Legislative office, Judicial offices, and the Times Union Center.
Atlanta, Georgia - Atlanta's “Underground” actually represents the original surface level of downtown Atlanta; the present streets are in fact raised roadways (viaducts) built in the 1920s. The shopping center Underground Atlanta, taking advantage of the former street-level storefronts, covers six city blocks, and includes retail shopping and restaurants. It was begun in 1968, and re-opened in 1989 after a financially-forced closure. Underground Atlanta homepage
Chicago, Illinois - (Chicago Pedway) consists of approximately 4 disjointed tunnel systems, the largest covering about 10 blocks, connecting such buildings and transit stations as Metra's Randolph Street Station, the Chicago Cultural Center, the Macy's (former Marshall Field's) store at State and Randolph, Chicago Transit Authority's State Street and Dearborn Street subway stations, City Hall, and the James R. Thompson Center. Pedway Map
Crystal City, Virginia - An unincorporated residential and commercial area of Arlington County, Virginia next to Ronald Reagan Washington National Airport, Crystal City features an extensive underground city connecting its hotels, office buildings, and apartment towers and is lined with 173 shops, restaurants, banks, medical, and other services. Map/Directory
Dallas, Texas - (Dallas Pedestrian Network) has a network of tunnels connecting various buildings in the downtown area.
Walt Disney World, Florida (South-West of Orlando, Florida) has a network of tunnels utilized by its employees (Cast Members) for transportation between venues, rest, staff preparation, and first aid. Some of the rest facilities resemble a small hotel room complete with a small kitchen.
Duluth, Minnesota has a small network of skyways and tunnels connecting some buildings, including the Federal Courthouse and Convention Center (DECC).
Houston, Texas - The seven-mile Houston tunnel system is set about twenty feet below Houston's downtown street system, and is composed of a series of underground passageways which, with above-ground skywalks, link office towers to hotels, banks, corporate and government offices, restaurants, retail stores, and the Theater District. Only one building, Wells Fargo Plaza, offers direct access from the street to the Tunnel; otherwise, you must enter the Tunnel from street-level stairs, escalators, or elevators located inside a building connected to the Tunnel.
Irvine, California - A network of large tunnels running beneath the University of California, Irvine connects many of the campus' major buildings to a central utility plant.
Minneapolis and Saint Paul, Minnesota - There are three major systems consisting mostly of above-ground skyways in the Twin Cities. Minneapolis's skyway system covers approximately five miles with 62 skyways. St. Paul's skyway system connects buildings in a 30-block radius in the downtown core.  On the University of Minnesota campus, the Gopher Way connects most buildings and parking structures together using a number of skyway links and underground tunnels.
New York, New York - Several subway stations have direct access to one or more buildings. Additionally, most of the lower floor of Rockefeller Center qualifies as an underground city, as it features connections to subways, an extensive underground concourse, building connections, and several restaurants, all below ground.
Oklahoma City, Oklahoma - The Oklahoma City Underground, formerly the Oklahoma City Conncourse, named after its founder, Jack Conn, is an underground tunnel system connecting nearly all the downtown buildings in a 20-square-block area. The OKC Underground is one of the most extensive all-enclosed pedestrian systems in the country, extending three-quarters of a mile and connecting over 30 downtown buildings by tunnel or skyway. The original tunnel link was built in 1931 and the system was extended in the 1970s. Offices, shops, and restaurants line the OKC Underground system. It underwent a $2 million renovation in 2006-2007. Upon completion of the renovation, the Conncourse was renamed the Underground.
Philadelphia, Pennsylvania - There are several underground concourses in Center City built around and including parts of Suburban Station, Market East Station, the Market-Frankford Line, and Broad Street Line. It is possible to walk from 8th Street to 18th Street east to west and Arch Street to Spruce Street north to south.
Richmond, Virginia - There are a series of connected tunnels between state government buildings in the city of Richmond. Certain passageways are locked off but a good portion of the tunnels are accessible from different buildings. The purpose of the tunnels is not generally known; the two most common explanations are that they were built to allow people to move between buildings in inclement weather or that they were built as part of an emergency evacuation plan.
Rochester, Minnesota - The Mayo Clinic's various buildings in the downtown area are interconnected with tunnels and skyways. Various other businesses also exist along the corridors, including a number of hotels that often house clinic patients. It is often called a subway, although there are no underground rails in the city.
Rochester, New York- Nazareth College in the southeast portion of Rochester has an extensive underground network of tunnels leading from the dormitories to the major buildings on campus. Rochester Institute of Technology also has several underground networks connecting dormitories and academic buildings together.
Seattle, Washington - Several modern undergrounds and a historical tour exist. The main shopping district around Westlake has an underground connected with the bus tunnel. Another substantial corridor extends from Two Union Square to Rainier Square with connections to hotels, the 5th Avenue Theatre, and many retail shops along the way. The Seattle Underground Tour in Pioneer Square takes visitors on a humorous guided walk showing the original ground level of many buildings in that area.