Is There a River That Will Make You Immortal?

A woman goes to a bookstore in late 1920s and somebody gives her a copy of Alex's translation of the Iliad. She finds out that this bookseller dies. And then towards the end of the book she finds this manuscript and this manuscript is what the story is. Then we get the narration of a Roman from the like fourth century AD something like that third or fourth century Roman soldier. He tells this tale about seeing some enemy and after torturing him finding out information about the existence of a river that will make you immortal. So he sets off in search from that on the way he encounters Tragla Dites cave dwellers kind of stunted people who don't communicate with