With 3.4 million inhabitants, Madrid is the second-largest city in the European Union, and with about 45 museums, it is one of Europe’s most robust cultural centers. Landmarks in Spain’s capital city include Plaza Mayor, the Royal Plalace, the National Library, the Thyssen-Bornemisza Museum, the Reina Sofía Museum, and the Prado Museum, one of the most-visited museums in the world. If you want to see the best that Madrid has to offer, consult our list of 20 must-see landmarks and cultural destinations below.