Valley of the Fallen Kings

The Valley of the Fallen Kings is a valley in which runs a river that leads to the Isle of the Blessed. In this Valley there are giant stone statues of the ancient kings. People normally don't go there, being afraid of the magical presence in this area. In fact, hidden in the Valley there is the Crystal Cave. It's also possible that Morgana's hut lies in the Valley of the Fallen Kings.

Merlin first went through it on his way to the Isle of the Blessed to seek Nimueh 's help and save Arthur from dying, because he had been bitten by the Questing Beast (Le Morte d'Arthur).

On one occassion Merlin and Arthur were running away from a group of bandits. Arthur was pierced in the back by a poisoned arrow and became unconscious. In the Valley Merlin attempted to heal him with magic, but he was unsuccessful. Suddenly Taliesin, a deceased Seer, appeared to Merlin and healed the Prince. He then showed Merlin the Crystal Cave, where the young warlock had a premonition of Morgana killing Uther (The Crystal Cave).

Lancelot took the dying Merlin through the Vally of the Fallen Kings after he was touched by a Dorocha to try to make it to Camelot in time for Gaius to heal him (The Darkest Hour: Part Two).

Arthur, Merlin and the Knights of the Round Table were passing through the Valley of the Fallen Kings when they were ambushed by mercenaries sent by Agravaine and Morgana. A battle ensued and Merlin was wounded and struck unconscious by a bandit. Arthur and Merlin, after managing to escape the fight, spend the night hiding from the mercenaries. With the young warlock now more pale and unable to move freely, they continued their journey back to Camelot, but they once again encountered the mercenaries, which Arthur engaged in combat whilst Merlin looked on helplessly. As a fresh wave of mercenaries rushed towards Arthur, Merlin used the last of his strength to block their path by causing a rockfall. This resulted in Merlin 's capture (A Servant of Two Masters).

Trivia
This place has been labelled as a bad omen by Merlin, since something bad happens whenever his group goes through that particular area.