Official site: www.chenonceau.com
Spectacularly beautiful. Built across the river, it epitomises the châteaux of the Loire.
Be warned: it is extremely popular and, unless you go in the depth of winter, you are likely to be competing with the hordes. It is also quite expensive - but understandably so.
Note the grounds are also attractive and most of the grounds are free.
About 2 hours away by car.