Casa Batllo or House of Batllo is perhaps the most beautiful residential property ever built. Located on number 43, Paseo de Gracia, in the central region of Barcelona, the building is a major tourist and cultural attraction. Casa Batllo was built by Antoni Gaudi and receives more than a million tourists every year. Fun fact: There are almost no straight lines in the entire building as Gaudi did not believe straight lines were found in nature. Casa Batlló is open 365 days a year from 9.00 am to 9.00 pm (last entry: 8.00 pm). Casa Batllo has been recognized as a UNESCO Heritage Site.