Casa Batlló, built between 1904 and 1906, is Antonio Gaudí at his Modernist best. He recast the original facade of the house with a fantastical front wall that is wavy and covered with a mosaic of colored glass fragments and ceramic discs. The roof appears to be an animal's back whose spin seems to change colors as your eye moves from one end to the other. The interior has similar surprises like skylights shaped like tortoises' shells and a wooden bannister shaped like the spine of a huge animal. Take your time in discovering the engineering and design innovations.