This enclosure is located at the center of Ile aux Moines, towards the tip of Penhap.
It forms a flared arc open to the south-east, and measuring approximately 65m in its maximum length.
Made up of 34 monoliths, this set is remarkably well preserved.
It presents at its north-west end a menhir larger than the others, called "The Monk" because of its resemblance to a figure wearing a hood.
It has on its back small circular engravings called "cupules", characteristic of the Neolithic period. Zacharie Le Rouzic reported in 1923 the presence of an ax engraved on one of the menhirs, but this was no longer observed.
A deposit of flint blades had been discovered in the center of the enclosure.
This monument should be compared to a giant menhir, now invisible because buried under buildings, located 30 m to the northeast.