Wookey Hole Caves is a cave system in Somerset, England. It doubled for the gold mines of Voga in 1975's Revenge of the Cybermen.
A month before filming took place a diver had drowned in the caves and when the crew got there, they were told stories about how several people had reportedly seen this diver "after death". There was a rock in the caves called "the witch" due to its distinctive features. The electricians dressed it up with a cape, a pointy hat and a broom. One and a half hours later, one of the electricians slipped off a rock and broke his leg. Two hours after that, Elisabeth Sladen's motorboat went out of control and she had to be rescued from the water by a stuntman who subsequently ended up in hospital.[1]