Casa Batllo is one of three unusual buildings along Passeig de Gracia, together with Casa Amatller and Casa Lleo-Morera which make up the "Block of Discord". The house was originally built for a middle class family and in 1904 Gaudi was commissioned to refurbish the building. Casa Batllo reflects Gaudi's playful side and the strange and fantastic style he is known for. The building can generally be classed as Modernisme or Art Nouveau but it is really in a league of its own.
Gaudi replaced the original facade with a work in glass and stone. The facade wall was made to curve and bend like a wave, this was then plastered and covered with a mosaic of colored glass and ceramic fragments. The top of the building looks like the back of an animal, generally referred to as a dragon. It appears to have scales and a spine adorned with round pieces of masonry which seem to change color as you look at it from different angles. Montjuic stone was used to create pillars on the first 2 levels; the thin pillars resemble the shapes of bones and are decorated with floral designs. The Noble Floor or main suite which faces the front on the building has a unique window system which opens and closes with counterweights. The projecting balconies resemble masks made of wrought iron. The façade uses organic shapes and colors.
The interior of the house is just as remarkable, there is a staircase banister which looks like the spine of an animal; a room which is decorated to look like it is under water; relief glazed tiles; a wooden elevator which still functions; a huge central skylight; stained glass; mosaics and unexpected details in many of the fittings. In all the building's ground floor, main floor, four self-contained floors, roof top terrace, loft and courtyard cover 5,000m².
Pedro Mila I Camps commissioned Gaudi to design the building on Passeig de Gracia; this was to be the architect's largest civil building. The unique structure has no straight lines, and no load-bearing walls, instead it relies on pillars and steel supports. The façade is self-supporting like a curtain wall. The irregular design includes ceilings which are of different heights. There are two courtyards which allow all the apartments in the building to get natural light through their windows. In all the building covers over 1000m². There are 9 levels including basement, ground floor, mezzanine, main floor, 4 upper floors and the attic. Gaudi added underground parking which was another bold move for his time.
The building exterior has undulating wrought iron balconies resembling waves; these were designed by Josep Maria Jujol. The building exterior is not as colorful as his other creations as it was left in its natural stone. The irregular shapes and stone color caused locals to nickname the building "the quarry" or La Pedrera.
Visitors can visit the attic and the floor top where the unusual design is consistent with the exterior. Gaudi made use of Art-Nouveau and Catalan modernista architectural styles. The roof top chimneys have surrealistic colors and resemble science fiction warriors and other fantastical characters. The chimneys were functional but also so decorated with mosaics, marble pieces and shapes that they are more like sculptural works of art.