François I began building the great Renaissance hunting lodge at Chambord in the early 16th century, but all told he spent only 72 days there and then only a few days at a time. The largest of all the Loire chateaux, it is best known for its unique double spiral staircase, designed or at least inspired by Leonardo da Vinci. The two spirals never meet over three floors, allowing people to come and go without seeing each other.

chambord.org