Athens: It opened on 27 February 1869 and serves the Athens urban area.

Boston: Opened on 1 September 1897, it is operated by the Massachusetts Bay Transportation Authority (MBTA).

Budapest: Budapest Metro opened in 1896.

Chicago: It opened on 6 June, 1892. Apart from the city of Chicago, it serves some of its surrounding suburbs in the state of Illinois.

London: Opened on 10 January 1863 as the world's first underground passenger railway. It is also called London Underground or the Tube.

New York City: It opened on October 27, 1904 and is one of the world's oldest public transit systems.

Paris: Inaugurated on 19 July 1900, it is known for its density, territorial limits, uniform architecture, and historical entrances.

Philadelphia: Opened in 1907, it is an urban rail transit network in and around Philadelphia, Pennsylvania, United States.

Glasgow: Glasgow Subway opened on 14 December 1896. It is an underground light metro system in Glasgow, Scotland.

Berlin: It opened on 15 January, 1902. It serves 175 stations spread across 9 lines with total track length of 155.64 km.