Castle of the Ancient Kings

The Castle of the Ancient Kings is where Arthur hid when Morgana became queen. It is where Percival, Lancelot, Gwaine and Elyan were knighted (The Coming of Arthur). That's also where the the rount table is located, to which Arthur, along with the knights of Camelot, Merlin, Gaius and Guinevere sat the night before Morgana's first overthrowal.