The ancient Greek mystical world was ruled by a small group of gods called the Olympians. When things had to be decided, the council of 12 gods met on Mount Olympus to discuss things.
All the Olympians kept a home on Mount Olympus. Unless they were off traveling somewhere, that's where you could find most of them. Hades preferred his home in the Underworld. Poseidon preferred his palace under the sea. But the rest of the Olympians lived on Mount Olympus.