Penglaouic menhir, Granite menhir in Loctudy, France.

The Penglaouic menhir is a granite monolith standing on the coast between Loctudy and Pont-l'Abbé that rises about 3 meters in height. The single stone rises from rocky ground and is surrounded by seawater at its base.

This megalith was erected about 5000 years ago roughly 2 kilometers inland and originally marked the source of a small stream. Over the course of millennia, coastal erosion and natural shifts transformed the landscape, leaving the monument now near the water.

The name Penglaouic is of uncertain meaning. Old cadastral maps label the stone simply as men or menhir, Breton for stone or long stone. Three Breton readings have been proposed: pen glaou, 'black head', perhaps for the coal tit; pen laou, 'head of lice', for the lichen on its top; or pen Laouic, 'Guillaume's head', after a nearby resident.

The monument becomes partially submerged during high tide, so low tide is the best time to visit and see it fully exposed. The site is directly accessible from the shoreline, so pay attention to tidal times and weather conditions.

In 1912 Commander Devoir measured the stone at 4.90 metres above the lowest tides; silting has since cut its exposed height to about 4 metres, and at high tide it is half submerged. Its base now sits roughly 0.75 metres below mean sea level, though it was raised on dry ground in the Neolithic.