See Wikipedia for a general introduction. The design is quite formalised having three common concentric boundaries.
- an inner chamber that is circular
- an outer kerb of standing stones
- a stone circle.
The main sub-type has a passageway connecting the inner chamber oriented somewhere between the south and the south west. The other type has no passageway and the classic site is Balnuaran of Clava with two passageway ring cairns, oriented identically towards the midwinter solstice sunset, and above them but between, a ring cairn with no passageway and a larger inner ring.