The central area of Budapest along the Danube River is classified as a UNESCO World Heritage Site and has several notable monuments of classical architecture, including the Hungarian Parliament and the Buda Castle. The city also has around 80 geothermal springs, the largest thermal water cave system, second largest synagogue, and third largest Parliament building in the world. Budapest attracts around 12 million international tourists per year, making it a highly popular destination in Europe. It also topped the ''Best European Destinations 2020'' list by Big7Media. Budapest also ranks as the third-best European city in a similar poll conducted by ''Which?''.