Usually referred to as La Pedrera (The Stone Quarry), with a wavy, curving stone facade that undulates around the corner of the block, Casa Milà is one of Gaudí's most celebrated yet initially reviled designs. Topped by chimneys so eerie they were nicknamed espantabruxes (witch-scarers), the building was unveiled in 1910 to the horror of local residents. The sudden appearance of these cavelike balconies on their most fashionable street led to the immediate coining of descriptions such as "the Stone Quarry" -- or, better yet, "Rockpile" -- along with references to the Gypsy cave dwellings in Granada's Sacromonte. Other observers were undone by the facade, complaining, as one critic put it, that the rippling, undressed stone made you feel "as though you are on board a ship in an angry sea." Seemingly defying the laws of gravity, the exterior has no straight lines and is adorned with winding balconies covered with wrought-iron seaweedlike foliage sculpted by Josep Maria Jujol.

The building was originally meant to be dedicated to the Mother of God and crowned with a sculpture of the Virgin Mary. The initial design was altered by owner Pere Milà i Camps, who, after the anticlerical violence of the Setmana Tràgica (Tragic Week) of 1909, decided that the religious theme would be an invitation for a new outbreak of mayhem. Gaudí's rooftop chimney park, alternately interpreted as veiled Saharan women or helmeted warriors, is as spectacular as anything in Barcelona, especially in late afternoon when the sunlight slants over the city into the Mediterranean. Inside, the handsome Espai Gaudí (Gaudí Space) in the attic has excellent critical displays of Gaudí's works from all over Spain, as well as explanations of theories and techniques, including an upside-down model (a reproduction of the original in the Sagrada Família museum) of the Güell family crypt at Santa Coloma made of weighted hanging strings. This hanging model is based on the "Theory of the Reversion of the Catenary," which says that a chain suspended from two points will spontaneously hang in the exact shape of the inverted arch required to convert the stress to compression, thus structural support. The Pis de la Pedrera apartment is an interesting look into the life of a family that lived in La Pedrera in the early 20th century. Everything from the bathroom to the kitchen is filled with reminders of how comprehensively life has changed in the last century. People still live in the other apartments.