There are many of these stone circles and other signs of long gone ancient culture on Bodmin Moor. This one is just south of an old China Clay quarry workings called Stannon works so, although not named on the OS map as such, most know them as the Stannon stone circle. This is a large (43 meters across) circle of around 70 stones, around a metre tall on average and mostly still standing.
You can go around the stones and roughly work out your compass orientation by looking to see which side of them the lichens have made their preferred home. With lichens favouring darker and damper conditions (like moss on trees in woodlands too), their growth will be much stronger in the shade of the cooler north side of the stones instead of facing the sun.
There is a suspicion that this circle is placed within the sight of the summit of Roughtor, the nearest and most obvious peak, so that the sunrise on the festival of Beltane appeared to originate from the top of the Tor.