Our guide, Chris Eley, wanted to arrange an underground ride through the caverns.
Many old mines that the MOD (Minister of Defense) used during WWII (for ammo storage—really a cover operation for UFO research) are ridable and spelunkable, in Monkton Farleigh, where searching yourself is encouraged.
More info on Dark Places—also see the BBC artcile.
Real walking hills around there—we walked a mile or so up a one-in-four I suspect.