Sintra has an extraordinary concentration of palaces primarily because of its unique microclimate and its historical status as the summer retreat for the Portuguese royalty and aristocracy. Located in the cooling hills of the Serra de Sintra, the area is significantly cooler and more lush than the scorching streets of nearby Lisbon. Starting in the 15th century, the Portuguese kings built the National Palace, and by the 19th century, King Ferdinand II transformed a ruined monastery into the whimsical Pena Palace, sparking a "Romanticism" movement. This led wealthy elites and international millionaires to build their own extravagant estates, such as Quinta da Regaleira and Monserrate, to be near the court and enjoy the "eternal spring" weather. The resulting landscape is a dense collection of Moorish, Gothic, and Renaissance architecture, which earned the entire cultural landscape of Sintra a UNESCO World Heritage designation in 1995.