Mount Olympus

Mount Olympus is the highest mountain in Greece and the original location of Olympus, the traditional home of the Greek Gods. It is no longer the location of Olympus because, as Chiron explains, the city of Olympus has steadily moved west, following the center of power of "Western Civilization" over the centuries and is now in the United States of America. Olympus is currently is located far above the Empire State Building (600th floor), while the original mountain remains in Greece. In the The Lost Hero it is revealed that while Olympus moves with Western Civilization, the "roots" of the Olympians are still there.

It's possible, although not confirmed, that the original city of Olympus was abandoned by the gods when they moved and that they just built a new one in every new country, and since the very first Olympus was here (and may still be here), it must be destroyed to fully dispose of the gods.