Cornwall is one of those counties where a field without an ancient monument is an empty field indeed. Given my penchant for hanging around ruins, this works pretty well for me, and I'm always happy to stop and take a look around if we're passing somewhere that seems interesting. Stone circles are always a draw, and we had a particularly gorgeous day for this one, the blue sky dotted with fluffy clouds which make photography a dream.
Consulting the map after the fact, we concluded that this was the ring known as the Merry Maidens. Should you wish to track it down for yourself, it's just off the B3315, about mid-way between Penzance and Land's End.
If you like this kind of thing, you might also be interested in similar circles we've enjoyed visiting in Scotland and Dartmoor.