La Sagrada Familia is one of Gaudí's most famous works in Barcelona. It's a giant Basilica that has been under construction since 1882 (that's not a typing error!) and it's not expected to be completed for some time yet.
Prague Castle is a castle in Prague where the Kings of Bohemia, Holy Roman Emperors and presidents of Czechoslovakia and the Czech Republic have had their offices. The Bohemian Crown Jewels are kept within a hidden room inside it.