I love storming castles so I can use all those lovely siege weapons but it is a costly exercize. Biggest I have done was a citadel - never dared take on a fortress yet.

Its great fun with bombard's when you've smashed down the walls and still have plenty of ammo to play skittles with the defenders who try to cover the gaps in the walls

The castles on high ground are nasty to take though Are there any castles with moats around them? I've seen water on the maps (lakes and rivers) but no moats. That would be really tough to attack.