Château de Chambord, France

Built between 1519 and 1547 as a hunting lodge for King Francis I, the Château de Chambord in the Loire Valley is the largest of the Loire châteaux and a masterpiece of French Renaissance architecture. Its iconic double-helix staircase — thought to be designed by Leonardo da Vinci — allows two people to ascend and descend simultaneously without meeting. The château has 440 rooms, 365 fireplaces, and 84 staircases spread across 5,440 hectares.