The Cavern of Despair was a supposed place thought to exist by the Klingons for those who had died and been forgotten.

In 2377, B'Elanna Torres recalled that she had not made a plea for her deceased Klingon grandmother L'Naan since she was a child to Kohlar. He then prayed to Kahless the Unforgettable himself to lift L'Naan and others from the Cavern of Despair and reveal himself to them in his full glory. Klingons believed that the dead could not rest in Sto-vo-kor if the living did not honor the memories of them and thus they would reside in the Cavern of Despair. (VOY: "Prophecy")