This feature is cool, you can actually lie inside it like a granite coffin.
I visited this site a few years back. I was maning a check point for an orienteering event.
Spent about 3 hours here. Even had a snooze in it!
Dr William Borlase, writing in 1754 , said:"Round Arthur's Bed, on a rocky Tor in the parish of North-hill, there are many [rock-basins], which the country people call Arthur's Troughs, in which he us'd to feed his Dogs."