It's a mix, but usually the real castles are on high ground when possible and the nearby village or town will be on half a klick or more away on flat land.
Here's a picture I took at one of the castles that shows the basic location and the names of many of the castles between Krakow and Częstochowa. It could be useful if you are looking to run a game in that part of Poland.
http://i1113.photobucket.com/albums/...psdy8l6m8u.jpg