Iv just got back from GO APE in the Forest of Dean and im absolutely knackered.
If anybody wants some good outdoors fun id really recommend doing this.
Its a tree top obstacle course
of which you have to secure your own safety harness to the different obstacles and then trek across it in order to get to the next platform. It has rope ladders, zip lines, Tarzan swings and cargo nets. It doesn't look much but its a 3 - 4 hour coarse and will tire you out by the end of it.
Kid friendly but adult punishing.
There are loads of different Go Ape Sites around the UK but i can only comment on the Forest of Dean venue.