In August Wilson's 2003 play Gem of the Ocean, the City of Bones is a strange, mystical city that Citizen Barlow must go to in order to deliver himself from his sins. The City of Bones is located in the Atlantic Ocean and it was built from the bones of the African slaves who died aboard the many slave ships that were transporting the slaves from their homes in Africa to America.
Citizen Barlow must go to the City of Bones to find salvation and redemption and to uncover his worth and his true self. He seeks redemption because he's responsible for the death of one of his colleagues at work, Garret Brown. Garret Brown lost his life as punishment for stealing a box of nails that was actually stolen by Citizen, who simply wanted to get back at his bosses for being exploitative and for using him. Thus, Citizen is technically to blame for the tragic and unjust death of his colleague—hence his journey of redemption to the City of Bones.
Aunt Ester, who claims to be 285 years sold, is the only one who can show him the way (both literally and metaphorically) and lead him there, as she represents the connection between reality and spirituality, Africa and America, and wisdom and mysticism.