"So his wyf, dame Igrayne, he putte in the castell of Tyntagil." Malory, Le Morte Darthur
Almost surrounded by the sea, Tintagel occupies a promontory on the northern coast of Cornwall and was, according to Geoffrey of Monmouth, were Arthur was conceived (and presumably born). Unable to take the castle of Tintagel by seige, Uther Pendragon is magically transformed by Merlin to resemble Gorlois, the Duke of Cornwall, the husband of the beautiful Igraine (Ygerna), whom he seduces. From that union Arthur is begotten.
"The castle is built high above the sea, which surrounds it on all sides, and there is no other way in except that offered by a narrow isthmus of rock." Given his description of the site, Geoffrey is likely to have visited it, himself. He is the first to mention Tintagel by name, which derives from the Old Cornish din or tin (fortress) and tagell (constriction or narrows) and probably associated it with earlier folkloric tradition that the site once had been the royal fortress of ancient kings. Certainly, it was a leading center of trade, Cornish tin being exchanged for oil, wine, and other luxury goods from the Mediterranean. Indeed, the sherds of imported pottery found at Tintagel are more than at all other sites in Britain and Ireland combined.
The ruins of these fifth- and sixth-century settlements may have been visible to Geoffrey. What is most prominent now, however, are the ruins of a castle built about 1230, by the Earl of Cornwall, the younger brother of Henry III. The location of this medieval castle had no strategic value and it is not known whether it even was used. But it does occupy the fabled birthplace of a legendary king.
(Tennyson, offended perhaps by the story of Uther's lust and deceit, has Arthur wash mysteriously ashore at Tintagel, to be found there by Merlin.)
The ruins, themselves, are less impressive than their location. The picture above is from Tintagel, itself, looking across the cove to the headland opposite.