The massive burial mound of a neolithic chieftain dating from 3800 BC, the astonishing Tumulus de Kercado lies just east of Kermario and 500m to the south of the D196; look for the signs. Deposit your fee (€1) in an honour box at the entry hut that you walk through to reach the site. You can walk through the passageway (there's a light switch) and stand up within the chamber at the heart of the tumulus.
The sacred geometry of the place is rather disturbed by a vast water tower alongside.