Gaudi's masterpiece, the Casa Batlló is one of the most unique residential buildings ever constructed in the Modernista style. Its facade bedecked with a rainbow of colored tiles gives way to the entrance hall that evokes an underwater sojourn complete with wave-like walls, turtle-shaped skylights, and a staircase that resembles the spine of a mythical creature. The upper level Noble Floor features windows that open out onto Passeig de Gràcia and are flooded with natural light and the connected outdoor patio is a kaleidoscope of hues wrought in glass and tile. From the terrace, it's easy to understand why the house is called casa del drac locally, as the roof tiles resemble Sant Jordi's dragon. A marvelous expression of both creativity and architectural acumen, the Casa Batlló stands as a testament to Gaudi's psychedelic genius.