Dating from around 4000BC, the St Lythans cromlech consists of three supporting stones capped with a large, flat stone, forming a chamber nearly 2m high. It was once covered with a mound that is now long gone.
As with many such pre-Christian/pre-Celtic sites, St Lythans has many local legends attached to it. It was once thought to be a Druid's altar and on midsummer's eve the capstone supposedly spins around three times. The field it stands in is known as the Accursed Field.
The site can be accessed from St Lythans village, which is around 6 miles southwest of Cardiff.