Ruined medieval chapel at Greeba in the parish of Marown.

St Trinian's stands in an arable field below the central hills. An antiquarian description placed it among a group of Manx chapels larger and more substantially built than the small keeills. Its windows terminate in simple Gothic arches formed from two long stones springing towards one another.

The chapel acquired one of the best-known Buggane stories on the Island. Tradition held that every attempt to roof St Trinian's was frustrated by a Buggane which tore the roof off during the night. In one telling, the creature complained that the sound of the church bells would disturb him and decided to amuse himself by tossing the roof away.

The story remained sufficiently current in the eighteenth century for Philip Moore, then curate of Marown, to try to disprove it. He masqueraded one night in the ruins to frighten local people and demonstrate the absurdity of their belief in the Buggane. According to David Craine, the performance got him into Bishop Wilson's bad books and did little to alter local opinion.

St Trinian's also appears in older lists of ecclesiastical baronies. The abbot or holder associated with St Trinian's was among those owing fealty within the Lordship of Mann, alongside the abbots of Rushen, Furness, Bangor and Sabal.