What is the journey that John takes in By the Waters of Babylon?
John takes a journey to the "Great Dead Place" in order to prove that he has what it takes to become a priest. He is the son of a priest, and appears to have obtained the most "magic" from his father, and for that reason is favored above his other siblings. He has accompanied his father on other priestly business, such as collecting scraps of metal and other trinkets from "dead places", where the technologically advanced civilizations of the past had lived.
On his journey, John realizes that the "Great Dead Place" is actually the area formerly known as New York City, and finds many interesting artifacts ranging from silverware to temperature knobs on a bathtub. He finds statues of George Washington, and crosses the Hudson River. Most importantly, howver, he discovers the remains of a dead human from the past... one of the "gods" as he would have thought. However, rather than finding a true god, he finds that those his people deemed as supernatural or godly are really just human like himself.
Upon his return, he informs his father of his findings. His father tells him that while he has discovered a great truth, perhaps it's not best to tell everyone else just yet, as this would lead to a devastating downfall of everything their primitive future society has been built upon.