Had fun finding this in the end asked the landlord of "The Star". He was less than helpful, saying such things as, "it has probably moved" and "you've got to be quick to find it". One local drinker when asked where is the Wimblestone said, "Thats where they play tennis in't it?". Eventually they told me, and here are the pictures.
Zebedee Fry were coming home late from the hay-making above Shipham. It were full moon, for they'd worked late to finish, and the crop was late being a hill field, so he had forgot what night 'twas. He thought he saw something big and dark moving in the field where the big stone stood, but he was too bone-weary to go chasing any stray bullock. Then something huge and dark in field came rustling all alongside lane hedge, and Zebedee he up and dive into the brimmles in the ditch till it passed right along, and then he ran all a-tiptoe to reach Shipham. When he come to the field gate he duck two-double and he rush past it. But, for all that, he see this gurt stone, twelve feet and more, a-dancing to itself in the moonlight over top end of field. And where it always stood the moon were shining on a heap of gold money. But Zebedee he didn't stop for all that, not until he were safe at the inn at Shipham. They called he all sorts of fool for not getting his hand to the treasure - but nobody seemed anxious to have a try - not after he'd told them how nimble it danced round field. And nobody knows if 'twill dance again in a hundred years. Not till there's a full moon on Midsummer Night.
This was told to Tongue by a schoolfriend, who'd heard it from her Mendip great grandmother, who was 90 at the time.
Another story about the Wimblestone - from Gray Usher's article 'Spade and Plough', as reported in Third Stone 25 by Phil Quinn.
On one of the Wimblestone's midnight rambles it felt tired and lay down for a rest. In the darkness a farmer mistook it for a cow escaped from his field, and encouraging it to move, gave it an thwack with his stick. The stone was infuriated, and reared up and rolled at the terrified man. He was forced to run to Rowberrow churchyard - the stone couldn't enter the consecrated ground and had to pace up and down outside the gate all night waiting for him to come out. In the end dawn broke, and 'Wimble' was forced to roll home unavenged.
The Wimblestone / Wimble Stone stands in a field at Pylle Well, to the NW of the Star Inn. It's 5'6" high, 6'2" broad and 18" thick.
Legend has it that it can move (wimble means giddy or lively - though it's also the name of a stonecutter's tool for boring holes, and the stone does have a hole). On nights when there's a full moon or on Midsummer's eve (especially both) it goes dancing round its field. Underneath it is said to be a pot full of gold.
One day a farmer decided to move the stone, so he chained it to two of his horses. They struggled all day but had to give up, exhausted. That evening the stone leapt up and roamed across the Mendips to the nearby Water Stone near Wrington to tell it all about how stupid the farmer was. The Water Stone always contains water in the hollow of the capstone, and the Wimble Stone had a good drink before returning to its own field.
[I imagine I read this in Grinsell's collected 'Folklore of Prehistoric sites']