Prado Museum

The building was never supposed to hold art. Charles III commissioned architect Juan de Villanueva in 1785 to design a Natural History Cabinet — a temple to science, not painting. Then Napoleon invaded, the Peninsular War trashed the construction site, and the half-finished building sat abandoned for years. When Ferdinand VII finally opened it in 1819, his wife Maria Isabel persuaded him to fill it with the royal art collection instead. Science's loss was art's gain, and the Prado was born — with a first catalogue listing just 310 works.

Today the collection has grown to roughly 8,200 drawings, 7,600 paintings, 4,800 prints, and 1,000 sculptures. The museum can only display about 1,500 works at a time — roughly 14 percent of what it owns. The rest lives in storage, on loan, or in satellite buildings. Francisco Goya is the most extensively represented artist, with an entire wing dedicated to his work, from luminous early tapestry cartoons to the nightmarish Black Paintings he smeared directly onto the walls of his own house in his old age.

But the Prado's crown jewel is Velazquez's Las Meninas, painted in 1656 — a painting of a painter painting the king and queen while the princess and her attendants look on. It's a hall-of-mirrors puzzle about who's watching whom, and it still stops people in their tracks after nearly four centuries. Hieronymus Bosch's Garden of Earthly Delights, a triptych of heavenly pleasures and hellish torments from around 1500, is the other must-see — acquired by Philip II, who was allegedly so obsessed with it he had it hung in his bedroom.

In 2007, Pritzker Prize-winning architect Rafael Moneo completed a major expansion, adding 22,000 square meters of new gallery space. The Prado keeps growing, just like it always has.