The Château of Chantilly is fairly easy to get to from central, on either RER line D (45 mins) or the main line train from Gare du Nord (25 mins), then a 20 minute walk to the grounds.
The Château itself is really beautiful, it’s surrounded by a moat and looks like it’s floating – and the still water gives an amazing reflection of the Château. The castle was actually used in the James Bond movie A View to a Kill!
There are also large gardens there, landscaped by the same man as the Palace of Versailles. We spent most of the day wandering around outside along the Grand Canal, and even found some Kangaroos!
One thing I would do in hindsight is remember to bring a packed lunch…There are two restaurants there, which are pretty exclusive and very expensive. We managed to get a table at one of these, where we had apple pie and Chantilly cream, which although delicious was slightly spoiled by the terrible service we received and extortionate prices…