Sintra is known for its many 19th-century Romantic architectural monuments, which has resulted in its classification as a UNESCO World Heritage Site. Although its heritage in buildings and nature is the most visible face of the historic individuality of Sintra, a whole literary heritage has made the area a legendary reference in Portuguese culture. It has become a major tourist centre, visited by many day-trippers who travel from the capital Lisbon. In addition to the Sintra Mountains and Sintra-Cascais Nature Park, the parishes of the town of Sintra are dotted with royal retreats, estates, castles and other buildings, including the mediaeval Castelo dos Mouros, the Pena National Palace and the Sintra National Palace.