As the centre of power of the Austro-Hungarian Empire Vienna was one of Europe's most powerful cities of the 19th century. The Old Town bears architectural witness to the rule of the Habsburgs and has been declared a UNESCO World Heritage Site. During its heyday Vienna was home to many of Europe's greatest musicians; it is also home to some of the best examples of Art Nouveau architecture, among them the building of the Secession museum. Unusual buildings include the Hundertwasserhaus, architectural testament to the dream of an alternative living that haunted the eighties of the last century. Vienna is also world-renown for its coffee houses.