Chapelle Saint-Tremeur sits a short walk north of the town centre at Prat An Ilis, set back from the coast in quiet fields. Built by the lords of Kergoz in the first half of the 15th century, it mixes Romanesque, Gothic, and Flamboyant Gothic elements in its window tracery and nave arcades, a characteristic Breton blend that reflects a building constructed over several decades. The nave and side aisle are separated by sturdy stone columns, and the interior is plain but atmospheric.
The chapel was inscribed as a Monument Historique in 1935 and underwent a thorough restoration in 2009-2010. It formerly depended on the parish of Plomeur rather than Guilvinec itself, a reminder of how fluid parish boundaries were in medieval Brittany. The chapel yard, with its pair of Iron Age stelae, is worth lingering in. These upright stones predate the chapel by well over a thousand years and hint at the deep history of settlement on this coastline.