Directions: From Shap take the turning on the left signposted Shap Abbey (E.H. site). Then take the first turning on the right (keep an eye out for the barrow just before the turning) and the Thunder Stone will come into view just beyond the farm turning on your left hand side.
There doesn't appear to be any public right of way to the stone and I would imagine you would need to ask permission at the farm. Otherwise, do what I did and view from the lane – easily seen.
... when the waste or common lands were enclosed by act of parliament about [thirty years ago], most of the stones of which this remarkable monumental curiosity was composed were blown into fragments by the power of gunpowder, and employed by the inhabitants in erecting rude stone fences [...]
The quality of these stones is a species of granite, reddish, and full of large white shining specks of spar-like appearance. When polished, some of them are veined, and have an ornamental appearance. There is no regularity in their shape, and few of them present sharp angles; indeed for the most part they seem from their rounded forms to have been long subjected to the action of water.
This species of stone is called by the country-people thunder-stone, but upon what authority seems a matter of much doubt. I have heard the inhabitants assign two reasons - one, that the stones have fallen from the clouds during thunder-storms; and the other, in consequence of their giving out sparks of fire when struck against each other, at the same time emitting a faint smell of sulphur. But in fact the great majority of the people would not be able to assign any reason for so singular a name, not trougling themselves to inquire into the origin of names.
From 'The Druid Stones near Shap, in Westmoreland' - from a Correspondent in vol 9 of The Penny Magazine of the Society for the Diffusion of Useful Knowledge (1840).
"Fear no more the lightning flash,
Nor th' all-dreaded thunder-stone;
Fear no slander, censure rash;
Thou hast finished joy and moan.
All lovers young, all lovers must
Consign to thee and come to dust"