Mount Othrys was the base of the Titans during the First Titan War and the Second Titan War. In the First War, it was assaulted by the Olympians, where Zeus used Kronos' Scythe to cut him into a thousand pieces, and cast him into Tartarus. Mount Othrys was located on Mount Tamalpais in Marin County.
When Percy Jackson, Thalia Grace, and Zoë Nightshade find Artemis (who had previously been missing), she is trapped under the sky by Atlas next to the growing ruins of Mount Othrys. Atlas fights against Percy, who then takes Atlas' burden (the sky) from Artemis so that she can join the fight. Zoë tries to protect Artemis from her father, Atlas, but in his rage, he threw her into the ruins eventually leading to her death.
Mount Othrys is in the process of being restored, with the Titan fortress on the top. Kronos returns to the mortal world, in the host body of Luke, due to Ethan Nakamura swearing allegiance to Kronos and renouncing the gods. However, Rachel throws a blue hair brush at him and Luke regains control and yells in pain, allowing the others to escape.
Following the defeat of the Titans, Hermes tells Percy that Mount Othrys faded on its own after the Titans were beaten and Krios had gone into hiding. But the next book begins the new series reveals that was just a cover-up.
It was revealed that the Roman demigods assaulted Mount Othrys during the Battle of Manhattan and destroyed the palace. Jason Grace, demigod son of Jupiter, was personally responsible for toppling the Black Throne and helped bring down Mount Othrys' and the Titan guarding it, Krios. Jason remembers this near the end of his mission with Piper McLean and Leo Valdez. The campers of the Greek Camp Half Blood were led to believe that it crumbled due to the defeat of Kronos, but they found out when Jason revealed it to them after remembering it. Jason also led the Romans into battle as praetor.
Towards the middle of the Percy Jackson and the Olympians series, it seemed as if Luke, under the influence of the Titan Lord, Kronos (father of time and the Olympians), raised Kronos from the depths of Tartarus in the Underworld. Kronos wanted to retake the control of the power of Ancient civilization from the gods and return humankind to the time when he was the Lord of the Titans. His plan was to wage war on the Olympians, and by going to New York City, where the Empire State Building and Olympus are located, he could destroy their seat of power.
However, with the help of the demigods from Camp Half-Blood and nature spirits, the Olympian gods managed to both defeat Kronos and the monster, Typhon. Mount Othrys was destroyed by the demigods of Camp Jupiter.
According to Percy Jackson's Greek Gods, Kronos' Palace on Mount Othrys was so huge and terrifying, that even Zeus' "jaw dropped" after seeing it for the first time. The palace itself, which reminds Percy of a very oversized mausoleum, is made completely from black marble, which, according to Percy, made it both "terrible and beautiful, made of fear and shadow." The palace's glimmering black towers reached the clouds, like "greedy fingers, reaching out for the stars." Percy describes the Mist surrounding Mount Othrys as more powerful than usual, like a veil, between him and the lower half of the mountain.
As for the interior, the main pavilion is ringed with Greek columns, the floor is polished black marble (which is pure black and shiny, like a mahogany piano), and a cold wind always blows down the hallway. Greek Fire burns all day long in braziers along the walls, which glow against the marble floor. In-between the braziers are black marble statues of the Elder Titans. In the main hall, the huge Black Throne of Kronos (which Jason topples in The Last Olympian, as revealed in The Lost Hero) is located. In Percy Jackson's Greek Gods, the throne is described as being cut out of a gigantic piece of pure black obsidian, and encrusted with gold and diamonds. In the graphic novel adaptation, a large chamber contains a turret-like podium and one room contains Kronos' Sarcophagus with stone floors.
- As revealed in Percy Jackson's Greek Gods, Kronos' Palace on Mount Othrys was built by the Elder Cyclops, and the Hekatonknieres, all of whom Kronos had initially freed from Tartarus.
- Mount Othrys is the birthplace of all of the Elder Olympians, except for Zeus.
- Even though the Titans' stronghold on Mount Othrys is destroyed, Atlas is still left to hold the sky right next to it.
- As shown in Percy Jackson's Greek Gods, Kronos' palace on Mount Othrys looks so terrifying, that even Zeus' "jaw dropped" when he first saw it.
- Annabeth said that she could not live in San Francisco because Mount Othrys is right there, and it is not safe for a demigod to live there. This would have been a cover up as Camp Jupiter is located in that area.
- While Greek demigods thought that Mount Othrys just crumbled into ruins, Roman demigods thought that Kronos just disappeared, but actually the Greeks destroyed Kronos and his army, and the Romans destroyed Mount Othrys.
- The entrance to Camp Jupiter is based in San Francisco so the Roman demigods can keep an eye on Mount Othrys.
- In Greece, the original Mount Othrys is located a few kilometers south of Mount Olympus, but in America it is located on the other side of the country. This is probably so that the Titans could gain their strengths and build their palace far away from Olympus.
- It was originally taller than Mount Olympus, but after Zeus sheared the top off with a lightning bolt, Mount Olympus is now taller than Mount Othrys.