Casa Batlló is a modernist building located on Passeig de Gracia in Barcelona, Spain. It was designed by the famous architect Antoni Gaudí and was built between 1904 and 1906. The building is known for its unique, organic design and use of color, featuring a façade with a wave-like pattern, irregularly shaped balconies and window openings, and ceramic mosaics in a variety of bright colors. The roof is particularly striking, with an undulating shape that resembles the back of a dragon and is topped with colorful ceramic pieces. Casa Batlló is considered one of Gaudí's masterpieces and is now open to the public as a museum. Visitors can tour the building and learn about Gaudí's innovative architectural style, as well as see examples of his use of natural forms, vivid color, and intricate details.