1/ Castles were built for protection and shelter..
2/ At first they were built on hilltops or they built their own earth mound to put them on. The castles were easy and quick to build as they were made out of wood. They had a big tower for defense on top of the motte. After the year 1100 another change in the way castles were designed took place. The old square keeps were not so good because it was easy to dig underneath the corners of the keep and make it fall down. Instead they started building castles with one set of round walls. these were good because soldiers could see all around and also the castles were harder to knock down. The one weak spot was the gateway so gate houses were made very very strong with towers on each side and a drawbridge.
3/ Because they would have been VERY cold in the winter!!, and we are not at war any more (well, I guess some parts of the world are, which is sad!)
4/ The Dungeon....because I like ghosts and there would be lots in the dungeon.
5/ Castles changed a lot over the time, to make them stronger and less likely to be broken, they were originally made out of wood, but as time went by more stronger materials sourced, weapons were more advanced and sharp so they had no choice!!.
6/ in the 1200's they had a concentric castle which had two sets of walls, one inside the other. If the attackers broke in through the outer walls, they would be trapped in between the two walls and killed. I thought this was a good idea

Ben W