The circle consists of 38 unworked, differently shaped stones, up to three metres high and weighing 16 tonnes, most of which are made of slate. They face the smoother side inwards. Some had toppled over. Originally there were 42 stones that formed an oval with a diameter of around 70.0 metres. A 3.3 metre wide area at the northern end of the circle, formed by two large stones, probably served as the entrance. In 1853, the remains of three burial mounds were discovered in the stone circle.

The circle was probably built around 3200 BC, making it one of the earliest stone circles in Britain. It is also a very popular site, especially after the arrival of the railway in nearby Keswig, bringing daytrippers from the industrial north. As a reaction to visitors chipping of fragments from the stones as souvenirs, Castlerigg became a protected monument by law already in 1882.

Nevertheless, some parents still see the stones as a children's playground.