A stone similar in size to the Avebury stones that lays on top of of the earth to the side of the sarsen drift at the bottom of a natural ramp leading up to the high point of the down in the direction of Avebury.
It’s said it may have been destined for Avebury but never made it for some reason.
For me it’s a stone of significance due to it’s size, location and the story attached to it, it’s also the largest surviving (non buried) stone in that area, though a few lumps have been knocked off it.
Follow the Herepath up to the ridgeway, enter Fyfield down via the gate then carry on till you cross the gallops, follow the path into the valley then turn right following the course or the sarsen drift, to the right of the drift you’ll easily spot the Monster stone, to me it looks rather like a giant frog, well from a distance anyway.
Glad to see this stone has made it here Megadread, I agree about it looking like an enormous frog - this was the first stone I really looked at outside of Avebury on the first occasion I walked up to Fyfield Down. A few years back now but it blew me away at the time.