Budapest is the capital of Hungary and the country's principal political, cultural, commercial and industrial centre. Budapest became a single city occupying both banks of the river Danube with the amalgamation in November 1873 of right-bank Buda and Óbuda together with Pest on the left bank. The Buda Castle is the historical seat of the Hungarian kings. It was built on the southern tip of the Castle Hill, next to the old Castle District, which is famous for its Medieval, Baroque and 19th-century houses and public buildings. The Buda Castle - together with Andrássy Avenue, flanked by eclectic Neo-Renaissance palaces and houses featuring grandiose façades, staircases and interiors - is part of the Budapest UNESCO World Heritage Site, declared in 1987.