The Neolithic burial chambers of Trefignath

Trefignath Chambered Tomb is a Neolithic-era burial site near Trearddur, south of Holyhead on Holy Island, off Anglesey in Wales. From 1977 to 1979, excavations unveiled three separate burial chambers built in succession. The first, at the western end, had a simple square chamber covered by a circular cairn. The second was a rectangular chamber with a narrow forecourt, and the third was added to the eastern end with large entrance stones.

Sources: Wikipedia, OpenStreetMap, Wikidata, Wikimedia Commons