The Tolmen stone is a large boulder with a person squeezing through size of hole. It’s near the Scorhill Circle on Dartmoor.
Stories abound. Faithless women pushed through it (were the faithless men too fat or is this just another sexist activity?) and the guilty crushed as the hole closed in on them.
A more politically correct idea is that going through it cures rheumatic disorders – you’d have to be fairly cured before trying this. The side-effect leaflet would need to include broken limbs. Might stick to paracetamol.
Druids apparently thought it had cleansing properties and lowered sinners through the hole for purposes of purification in the waters of the Teign – perhaps falling through into the river did that anyway.
I think it may be time to recreate myths. Could this hole actually be a time-travelling portal? Other ideas?