The Dragon's Cave is a large underground cave beneath the Castle of Camelot in which the Great Dragon, Kilgharrah, was imprisoned by Uther Pendragon following the Great Purge. Balinor, a Dragonlord and Merlin's father, was tricked into helping Uther trap the dragon.
Some twenty years after the dragon's internment, Merlin arrived in Camelot, and the dragon began calling to him. Soon after, Merlin discovered the cave and the dragon (The Dragon's Call) and began visiting regularly for the creature's advice. Merlin later freed the dragon from the cave (The Fires of Idirsholas), fulfilling a promise he had made in exchange for Kilgharrrah's help and advice. Kilgharrah attacked Camelot in revenge for his imprisonment and the genocide of his race, but Merlin was able to stop him with his Dragonlord powers (The Last Dragonlord). Kilgharrah once again became Merlin's advisor and friend and a field outside of Camelot, where Merlin first commanded the Dragon, replaced the Dragon's cave as their meeting place (The Tears of Uther Pendragon).