Merlin's Cave is a cave located beneath Tintagel Castle, 5 kilometres (3.1 mi) south-west of Boscastle, Cornwall, England. It is 100 metres (330 ft) long,[1] passing completely through Tintagel Island from Tintagel Haven on the east to West Cove on the west.[2] It is a sea cave formed by marine erosion along a thrust plane between slate and volcanic rocks.[1] The cave fills with water at high tide, but has a sandy floor and is explorable at low tide.[3]
Tennyson made Merlin's Cave famous in his Idylls of the King, describing waves bringing the infant Arthur to the shore and Merlin carrying him to safety.[4]