The magnificent Château de Chenonceau in the Loire Vally in France.
A stately manor was built in the place as early as the 10th century and went through several incarnations. The castle was built in its present form in 1513 by Katherine Briçonnet, then made even more attractive by Diane de Poitiers and Catherine de Médicis, and saved from the rigours of the French Revolution by Mrs Dupin. Take the time to read some interesting history in the Chateau's own website. I was there in 2000 with a group from Tulsa Community College.