Casa Batlló is one of Antoni Gaudí's amazing buildings in central Barcelona. It was originally commissioned for Josep Battló i Casanovas as a residence for him and his family. The first 2 floors were intended for them and the top floors to be rented out.
Amazing as it may seem the main part of the building is still private residences, but the first floor (or second if you're American) is open to the public since the Gaudí year of 2002. Recently (2004) they have also opened the roof and the loft to the public, but I have not been there yet. Always something to look forward to.
The whole house has a very organic feel to it and to me it feels like entering an underwater world when you go in. There are a lot of absolutely marvellous architectural details, like the way you can adjust the amount of available light in the living room using coloured screens, or the fact that the windows are smaller higher up in the building to give an even light without letting in too much heat. That kind of attention to detail goes through the entire house.
Something that blew my mind is that there is not one single 90 degree angle in the house. Everything is curved and has odd shapes. When you on top of that realize that Gaudí himself didn't have a blueprint for the building, just a few hand made scetches and actually went around and instructed the workmen himself it's a miracle that the building was ever built at all.
My only disappointment when I was there is that you are not allowed to take photographs, not even without flash, and they have lots of very attentive guards on duty. I would have liked to take some of the lovely details home with me in my camera. The guide books never gives you exactly the right angle...