Casa Batlló is located at Number 43 Passeig de Gràcia, in Barcelona. It forms part of the island of buildings known as the "manzana de la discordia" (block of dissension) because its buildings belong to so many different architectural styles.

The owner, Mr. Josep Batlló, originally planned to tear down the building. He requested permission for this from Barcelona City Hall in 1901. But in May 1904 he made a new application requesting permission to totally remodel the house.

The main floor would become the home of Mr. Batlló and his family, and each of the other four floors would be divided into two flats to be rented out, just as Calvet had done in his home on Casp street.

The reforms included enlarging the building’s patio, changing the ground- and main-floor facade, crowning the roof and redistributing the dwellings’ interior spaces.

The interior patio was enlarged and covered with ceramic pieces designed by Gaudí. They are dark blue at the top, and their hues get progressively lighter toward the ground floor, eventually reaching white. This achieves better distribution of the natural light.

The solution which Gaudí devised for the facade kept builder José Bayó awake for three nights, since it was totally propped up until the new, thin columns, made from sandstone from nearby Montjuïc, were prepared to replace the original buttresses.

The windows of the main floor gallery were enlarged, and their new appearance provoked a nickname for Gaudí’s new work: "la casa dels Badalls" (House of Yawns). Another name it received was "la casa dels ossos" (House of Bones), due to the similarity of the gallery’s fine columns with a skeletal structure.

The balcony tiles were replaced with curved-base balconies and, on top of this, the famous railings which have originated so many interpretations were placed.

On the top floor we find two elements which break with the facade’s symmetry: a terrace and a tower. At first, Gaudí wanted to place the tower in the center of the upper part of the facade, but he realized that if he placed it there, it would overpower the facade of the neighboring Casa Ametller, built by Puig y Cadafalch, and affect its beauty. So he moved it and depressed the left part of the facade by building the small terrace. The tower is covered with pieces of glass; engraved with the monograms of Jesus, Mary and Joseph; and crowned by an ivory-colored cross which was created in Mallorca. When the cross came out of the kiln it cracked, but Gaudí said that he liked it that way even more.