Probably about 30 minutes by car. There is the ruined castle and a smaller more modern building (tudor I think) which is intact, also an indoor menage where they occasionally have horsemanship displays.
We've been a couple of times as we are EH members and get in free.
If the horse displays are on when you visit it's essential to pre-book tickets, we saw one and were very impressed even though we are not at all "horsey" people.
Fabulous views over the countryside from up there, not much else in the town of Bolsover that I can remember.