Chambord is the biggest of the royal chateaux in the Loire valley. It was built by King Henri I (Wiki here) as a hunting lodge. This was appropriate as it is situated in the forest of Chambord. You drive through the forest to get to the chateau.
The chateau is big and to do it justice, a whole day is needed to view it.
There is a walkway around most of the roof from where the sights are impressive. This is reached by way of a double helix staircase that is said to have been designed by Leonardo Da Vinci. This alone is worth a vist to Chambord.
The Wiki for Chambord is very good and you can find it here.