The Jewels of Aptor
by Samuel R. Delany
It is a post-atomic future and civilization has regressed to a Middle Age like world. Geo a young student and poet, takes a job on a boat with a strange passenger, a priestess of the goddess Argo. They are heading toward a land of mutants and high radiation, Aptor, to recapture her daughter who has been kidnapped by the forces of the dark god Hama.