I was at Ham Hill last year. There was a big historical festival up there, with lots of local schools involved in a drama involving giant puppets, showing the history of the area, us medievals, a Roman group, and other stuff going on as well.
The hillfort is immense! It also has a quite reasonable pub inside it, on the hill top. The part where we were camped had also been a quarry - which made it a bit difficult to pitch the tents! (about an inch of topsoil followed by solid rock).
We're going to be back next year for their historical festival.

South Cadbury is wonderful, too. We went up there years ago, just after dawn. There was low-lying mist, and we watched the local rabbits show their total contempt for a young fox - not bothering to hop out of the way until it was almost on top of them. South Cadbury has a rich and varied history, with masses of archaeology - dug by Leslie Alcock in the sixties - and it was certainly occupied at the right time to be an original for Camelot.