Mount Olympus is a celestial realm where the Olympian Gods of Greek myth famously reside and the 12 Olympian gods and goddesses of the Olympian Pantheon held court.
Described as "a paradise set above the clouds that only the gods could ever reach" the realm was original set atop the mountain of the same name in northern Greece. Once ruled by the Titans of Myth until their children, the Greecean Gods lead by Zeus, usurped them and cast them into Tartarus, the gods built their own homes and palaces within the mountainous realm's gorges and oversaw the mortal world from their home, although they would sometimes venture forth into the mortal realm for their own ends.
The Olympians rule over the realm was uncontested until the God of Monsters Typhon, with the help of the other monster gods, challenged Zeus for control. Most of the gods fled in fear, but a few stayed, including Athena and Nike. Together, the gods managed a victory after the hardest battle ever fought in Greek mythology.
Following the Millennium incident, where a Manhunter murdered Pan and impersonated him to manipulate Zeus, Darkseid invaded Olympus. However, he missed the Olympians who had left the realm for a conference with Poseidon and Hades and was driven out of the realm shortly afterwards by Superman and Wonder Woman.
Never-the-less Darkseid left the realm corrupted and in a state of destruction but instead of rebuilding, the gods decided to conduct a "cosmic migration" across the other celestial realms; calling on the Amazons of Themyscira to destroy what remained of the Olympus realm.
The effect of the absence of their gods' power in the Earthly realm led to the Amazons gradually
While any of the divine gods of ancient Greece could live on Mount Olympus, no mortal was ever allowed admittance to the realm. Most often this rule was subverted by the gods by turning the mortals they wished to enter the realm into divine beings. This rule was once put to the test when the mortal Bellerophon tried to ride the winged horse Pegasus up to Olympus. However, Zeus sent a mere gadfly to attack Pegasus, who kicked and reared and accidentally threw Bellerophon from his back; severely injuring his legs and going blind from the fall.