The city is the seat of a Roman Catholic archdiocese (left bank of the Vistula) and diocese (right bank), and possesses various universities, most notably the Polish Academy of Sciences and the University of Warsaw, two opera houses, theatres, museums, libraries and monuments. The historic city-centre of Warsaw with its picturesque Old Town in 1980 was listed as a UNESCO World Heritage Site. Other main architectural attractions include the Castle Square with the Royal Castle and the iconic King Sigismund's Column, St. John's Cathedral, Market Square, palaces, churches and mansions all displaying a richness of colour and architectural detail. Buildings represent examples of nearly every European architectural style and historical period. Warsaw provides many examples of architecture from the gothic, renaissance, baroque and neoclassical periods, and around a quarter of the city is filled with luxurious parks and royal gardens.