The 2nd oldest metro in the world and also a World Heritage is this line from Vörösmarty square to the City Park in Budapest.
World heritage place:
Andrássy Avenue and the Millennium Underground (extension to "Budapest, the Banks of the Danube and the Buda Castle Quarter") (C ii, iv)
The World Heritage site is extended to include the site of Andrássy Avenue (1872-85) and the Millennium Underground railway (1893-96) in Budapest, built in the second half of the 19th century as part of the celebration of the centenary of the Hungarian State. The scheme is a representative example of the implementation of planning solutions associated with the latest technical facilities of the day to meet the requirements of an emerging modern society. ” UNESCO