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. (DOC: The Tin Men and the Witch)
The same cave system was used again three and a half decades later, by the BBC Wales team, for The End of Time. It was in Wookey Hole Caves, passing for the Ood Sphere, that the Tenth Doctor is taken by Ood Sigma, to speak to the council, where he finds out that the Master has returned.