Weekend cheap/free activity for bored boy!

[FedupofTurkey]

I'm looking for an activity to keep an 8 year old boy out of mischief! It needs to be free/cheap, I can drop off and leave for a couple of hours on a weekend. He's not particularly sporty but is a climber/gymnastic type. Any ideas?

are you anywhere near a climbing wall? our local ones do a saturday club which costs about a fiver a week. Other than that check out what your local library has to offer (ours do sat morning sessions, free) and also think about cinema kids club - something utterly daft like £1