An underground electric railway, 3.7 km in length, was opened in Budapest in 1896 to convey visitors to the exhibition staged in that year to mark the millennium of the Hungarian nation. The Millenium Undergrund line, now called M1, was the nucleus of a much larger Metro network serving the city and its suburbs that grew up during the 20th century. The line is part of 'Andrássy Avenue and its historic environment', which was inscribed to Unesco World Heritage List in 2002.
The Underground Railway Museum is located in the former terminus station, which was converted to an exhibition hall in 1975, and is accessed from the pedestrian subway that serves the platforms that are now in use. The principal exhibits are passenger carriages that date from the opening of the line, and others used on the Budapest Metro in the 20th century. There are also displays of posters and photographs illustrating, amongst other things, the construction of Metro lines M2 and M3. The museum was renovated in 1996 in commemoration of the centenary of the Metro.