In The Lightning Thief, the first book of the Percy Jackson and the Olympians series, Percy must take a cross-country trip from Long Island, New York to Los Angeles, California to enter the underworld. He cannot take a plane because as the son of Poseidon, god of the sea, he is unable to travel in the sky—Zeus's realm—especially while Zeus is already angry.

The cross-country trip takes Percy and his companions Annabeth and Grover by car to New York City, by bus to New Jersey (as they must escape the bus before it reaches its destination), by train to St. Louis and then to Denver, to a water park outside Denver due to a trick from Ares, by zoo delivery truck (upon which they hitchhike with the help of Ares) to Las Vegas, and then by taxi all the way to the Santa Monica pier in Los Angeles. After Percy communicates with a Nereid in the Pacific ocean, he, Annabeth, and Grover take a bus into West Hollywood to find "DOA Recording Studios," the front for the entrance to the Underworld. After a detour at "Crusty's Water Bed Palace," they find the "recording studio" and find themselves in an upscale waiting room where they bribe "Mr. Charon" into taking them across the River Styx. After getting across the river, they find themselves in an area much like a toll booth, including "EZ Death" stations, and guarded by the three-headed Cerberus. From there, they are able to trick Cerberus and find their way into the Underworld to meet with Hades.