The Moscow Metro is a metro serving Moscow, Russia, and the neighbouring Moscow Oblast cities of Krasnogorsk, Reutov, Lyubertsy and Kotelniki. Opened in 1935 with one 11-kilometre (6.8 mi) line and 13 stations, it was the first underground railway system in the Soviet Union. As of 2021, the Moscow Metro, excluding the Moscow Central Circle, the Moscow Central Diameters and the Moscow Monorail, has 241 stations and its route length is 412.1 km (256.1 mi), making it the fifth-longest in the world and the longest outside China. The system is mostly underground, with the deepest section 74 metres (243 ft) underground at the Park Pobedy station, one of the world's deepest underground stations. It is the busiest metro system in Europe, and is considered a tourist attraction in itself.