Merlin's Cave at Tintagel Castle in Cornwall. Tennyson made this sea cave famous in his Idylls of the King, describing waves bringing the infant Arthur to the shore and Merlin carrying him to safety. The lower portion of the steps down to the cave have been washed away, and it is necessary to clamber down some boulders to reach the beach. The cave fills with water at high tide, but has a sandy floor and is explorable at low tide.
"Siege de Merlin" - "Home of Merlin", in the Foret de Brocéliande, Britanny. The forest of Brocéliande is mentioned in Arthurian legend, & this area claims to be the mythical forest today. This rock formation is supposed to be where Merlin came to watch the sunset over the forest. Also allegedly the territory ruled over by Morgan le Fay, half sister of King Arthur. True history or tourist bait?