It originally opened with steam locomotives in 1863, with electric trains starting operation in 1890.
It was the first underground train service in continental Europe. The Tunel has remained in service since 1875, covering a short distance of 573 metres.
The Tunel, Istanbul
It started operation in 1892. The 24-hour service has an 165 km (approx.) long network.
Chicago elevated L metro system
The system runs along an underground 10.5km loop and is among the only metro systems to have expanded lines beyond the original route.
Glasgow Metropolitan Railway
It began operation with its Line 1 in 1896. The network covers 52 stations. The Line 1 of the Budapest Metro was declared a World Heritage Site by UNESCO in 2002.
Budapest Metro
The first line was inaugurated in July 1900. Today, the system has 16 lines covering a total network of 214km. Of this, 197 km of the network runs underground.
Paris Metro
The network comprises of 150 kilometers covering 175 stations around the city. It was used as bunker during the second world war.
The Berlin U-Bahn
With 420 stops in its network of 380 km, the New York City subway is the largest system in the world in terms of stations. It started in 1904.
New York Subway
It began operations in 1869 with tracks laid down for steam locomotive service. The underground tracks were later changed n 1904.
Athens
It is operated by the Southeastern Pennsylvania Transportation Authority (SEPTA) in Philadelphia, US. It started in 1907.