It took the neighbors a long time to warm up to Modernisme. When Gaudí’s last secular commission, Casa Milà, was finished in 1912, they took one look at the undulating lines of seemingly wind-eroded rock and dubbed the building La Pedrera (“the stone quarry”). The shock of its novelty has faded, but the nickname has stuck as a term of endearment. With a sinuous, rippling facade, it is one of the most beloved of Gaudí’s works, and is another spot where purchasing an advance ticket online will save you precious time. The tour includes the patios and the Espai Gaudí (loft and roof). But the best part is visiting the Pedrera Apartment, complete with Gaudí furniture. Substitute a modern music system for the Edison phonograph, and most visitors would be ready to sign a lease on the spot. The Espai Gaudí holds period photographs, drawings, and models that elucidate Gaudí’s design techniques. Gaudí may have been a genius, but he was no math whiz. To calculate the loads an arch could bear, he hung weights on knotted cord to get the shapes he wanted, then extrapolated to life size. Gaudí saved his grandest gestures for the rooftop, transforming functional chimneys into a sculpture garden of swirling mosaic forms and ominous hooded warriors. Gaudí intended that the roof be used as an open-air terrace, and during the summer, jazz musicians hold forth several evenings each week. Amid the chimneys Gaudí built a lovely parabolic arch to frame what would become the towering steeples of his masterpiece, La Sagrada Familia. La Pedrera offers special night visits called “The Secret Pedrera” with a very limited number of admissions.