The Passeig de Gràcia is a wide avenue which runs through the center of Barcelona and some of its most important neighborhoods. The richest families in Barcelona settled here when it was first built and, to show off their wealth, they commissioned homes by architects like Gaudi, Domenech i Montaner and Puig. These three architects each have a house on the same block, which was a bone of contention as the owners fought to have the most beautiful and most modern house. The Casa Batllo is one of Gaudi's most famous buildings and is now owned by a private organisation. Entry costs 16 euros, and is well worth it for the tons of information you can get from the audio guide.