The Metro 1 (Officially: Millennium Underground Railway or M1) is the oldest line of the Budapest Metro system.

Known in Budapest simply as "the underground" ("a földalatti"), it is the second oldest underground railway in the world (the first being the London Underground's Metropolitan Line), and the first on the European mainland. It was built from 1894 to 1896. In 2002, it was listed as a UNESCO World Heritage Site.