This building is so unusual that it seems as if it was designed by an alien, although, of course, its creator was a man - the great architect Antonio Gaudi. Built in 1906-10, famous Casa Mila, as well as the Sagrada Familia, is one of the most important works of Gaudi. Over a million people attend Casa Mila every year, so those wishing to see its interiors and visit the terrace have to stand in a queue. Don't want to wait? Buy online tickets securing a quick pass via Excurzilla.