Pridhamsleigh Cavern is a limestone cave on the outskirts of Ashburton, one of the few accessible wild caves in Devon and well known among cavers in the south-west of England. The cave system includes an entrance chamber and a series of passages leading to more complex sections, with stalactite and stalagmite formations of real quality.
Access is managed by the Devon Speleological Society — you need to contact them in advance to visit, and appropriate equipment (helmet, lamp, old clothes) is essential. This is not a show cave: there is no lighting and no guided experience. That is precisely its appeal. If you're willing to do it properly, the cave is an extraordinary thing to find in the middle of a Devon market town.