Though for the most part grounded in history, August Wilson's Gem of the Ocean contains a number of fantastical elements. One only has to think of the protagonist, Aunt Ester Tyler, being 287 years old.
Another fantastical element in the play is the City of Bones. This is a mythical place in the Atlantic Ocean built from the bones of African slaves. The Atlantic was the main route for the transportation of slaves from Africa to the United States. In the City of Bones, we can therefore see an intersection between the factual and the fantastical, the historical and the magical.
The City of Bones is a place of redemption where Citizen Barlow believes he can redeem his sins. And those sins are very serious indeed. Citizen is responsible for the death of Garret Brown. Brown died of drowning while trying to avoid arrest for the theft of a box of nails. As it turns out, it was Citizen who stole the nails as a way of getting back as his cheapskate employers. He is therefore morally responsible for Brown's death.
And so Citizen feels that he must go to the City of Bones. He will be guided in his journey by Aunt Ester, whose great age enables her to act as a link between past and present, between the real world and the spirit world, and between Africa and America.