You can't miss the Auberge de Castille, one of Valletta's most impressive buildings, perched at the city's highest point. This grand Baroque masterpiece now serves as the Office of the Prime Minister, so while you generally can't go inside, its magnificent facade is a sight to behold. From its position, you get a fantastic sense of the city's layout and stunning views over the Grand Harbour, making it a perfect photo opportunity and a key stop on any walking tour.