Famous for its impressive canal structure, Utrecht is the fourth largest city of the Netherlands. The inner city has retained its Medieval structure. Its skyline is dominated by the Dom Tower of Utrecht, belonging to the former cathedral. One of Utrecht's landmarks of modern architecture is the 1924 Rietveld Schröder House, listed on UNESCO's world heritage sites. The city also offers an active cultural life with several theatres, the classical music centre Vredenburg, several cinemas and many art galleries.