St. Louis, Missouri, U.S.A.
The Gateway Arch (also known as the St. Louis Arch) is a national monument in Missouri, USA. The nation’s tallest monument at 630 feet, the Gateway Arch has beckoned visitors for more than 40 years with its iconic, awe-inspiring shape. The vision of renowned architect Eero Saarinen, the Gateway Arch commemorates Thomas Jefferson and St. Louis’ role in the westward expansion of the United States of America.
While on their quest, Annabeth insists upon stopping at the Gateway Arch, because of the architecture. The group visits the underground museum, where Grover starts to feel that something is wrong. After there is no room in one of the elevators back down, Percy stays behind to take the next one. While alone he discovers that one of the other visitors was Echidna, the mother of monsters. Echidna was accompanied by her dog revealed to be the Chimera. After a short battle with no victory, Percy falls into the Mississippi River, where a messenger of Poseidon tells him to go to Santa Monica Beach.
After Frank and Hazel go to find Percy who had fallen off a glacier, he was sitting on a piece of ice waiting for them to return. When they make a comment about how far he fell, he claims it was nothing, and he fell at least twice as far from the St. Louis Arch, which shocked both Hazel and Frank.