Reachable by boat from the town of Larmor-Baden near the opening of Morbihan Gulf to the Atlantic Ocean, Gavrinis is an uninhabited granite rock outcrop of 750 × 400m.

The old Breton word Guerg is not related to gavr, but to parallels such as Welsh gwery, or Old Irish ferg, signifying "wrath".

At that time, the light wooden structures cladding its entrance were burnt, after which part of the mound collapsed, obscuring and blocking the passage.

The mass of stones forming the cairn is internally structured by a series of walls, subdividing it into separate "ranks".

A common horn-like motif may symbolise cattle, and a shape conventionally called the shield may be a very stylised human figure.

In 1984, it was discovered that the external side of some slabs, now covered by cairn material, is also decorated, but in a different style from their internal face.

The slab can be joined with the ceiling stones of two other monuments, the Table des Marchands dolmen and the Er Vinglé tomb, at Locmariaquer, at a distance of 4 km.

A replica of part of the Gavrinis passage with its decorated slabs can be visited in the museum at the megalithic necropolis of Bougon (Deux-Sèvres).