Cornelius Sigan's Tomb was located under Camelot and was discovered by the miner, Tom. Inside were a number of precious artefacts and jewels as well as the soul of Cornelius Sigan concealed in a heart, set on top of his coffin. There was also a trap which one miner released and was immediately killed by him.
The Tomb was later broken into by a servant named Cedric who became possessed by the soul of Cornelius Sigan. The soul attempted to possess Merlin but he was able to return it to its setting. It was later sealed to prevent anyone else from unleashing the soul (The Curse of Cornelius Sigan).