Between 1904 and 1906, Gaudí transformed a conventional building on Passeig de Gràcia into one of his masterpieces. Commissioned by the industrialist Josep Batlló, the house became a manifesto of advanced Modernism —an architecture where light, color, and organic forms blend seamlessly with nature. The façade, covered in "trencadís" (broken tile mosaic), changes tone depending on the daylight. Its iron balconies resemble masks or shells, and the columns of the main floor evoke bones, giving the building an almost marine or fantastical appearance. Inside, Gaudí designed every detail to optimize light and ventilation: from the vaulted entrance hall to the ceramic light well that distributes brightness gradually throughout the space. On the rooftop, the curved roofline and mosaic-covered chimneys crown the building with an almost sculptural character. Located on the so-called “Block of Discord,” Casa Batlló stands alongside other Modernist gems by Puig i Cadafalch and Domènech i Montaner, reflecting the bourgeois splendor of early 20th-century Barcelona.