Tresilian Bay, also Tresillian Bay, is a bay in southeast Wales, west of Llantwit Major's Collugh beach and east of St Donats, on the Bristol Channel. The beach at the bay lies in front of a valley in which the Nant Tresilian flows and empties in the sea. It lies along a stretch of coast and cliff path under protection by the Glamorgan Heritage Coast,[1] characterised by limestone cliffs with many caves and several bays/valleys.[2] There is a distinctive white house, Tresilian House, located at Tresilian Bay at the end of the valley in front of the pebble beach and a pill box on the cliff nearby. The cove of Col Huw is located nearby.[3]