Spent just over an hour wandering round the inside of the fort, pressing switches and stuff. Found a sign that said there were five switches, one “that goes back”, which I’m assuming is the “reset” one I found but didn’t touch. I think I’ve hit the other five now – I just need to make it back to a door that was locked before (and, I’m assuming unlocked now).
Had some real trouble to start with, as the baddies in the fort were a bit too strong for me, but now I’m at level 15 or 16 for all my characters, I can usually kill all the baddies off before they even get to attack. Beat is (or rather, was) dead though, but somehow has now regained 560-ish HP. I’m not sure how.