Castle Shadowgate is the titular castle that is encountered in Shadowgate and Shadowgate 64: Trials of the Four Towers. It is built on the Gatekeeper mountains in Kal Zathynn. It was the meeting point of the Circle of Twelve during the Age of Enlightenment.
The Castle Shadowgate was the most powerful castle of Tarkus as inhabited by the Druids. Composed of over 150 rooms, few are accessible to anyone but one of The Circle of Twelve. The walls of the castle are very much alive and obey the commands of the Druids; thus, secret chambers are abundant.
Shadowgate was also an extremely well-fortified castle; during times of war, it is the most secure place on Tarkus. During the Dark Years and the Rage Wars, Shadowgate served as the Kings' stronghold and proved to be the deciding factor in the Kings' victory.
Dissidia: Shadowgate[]
Lakmir was the survivor of the Hero Kings that were slewed by the warlock. They were able to seal him away to Shadowgate. Both it and Stormhaven were located in a world named Tyragon. Talimar belonged to some wizards, the Circle of 12, before he was the warlock, who was corrupt and wanted to break free hence summoned the Behemoth. Shadowgate's in a land called Kal Zathymn at the top of Gatekeeper Mountain.
During the crossover fic, this was the last destination for all the Cosmos warriors before they should be revived and returned to their own home worlds. Those 8 after being slewed by the Manikins, and the 9 others who won over Chaos. Cosmos summoned everyone there, excepting the Warrior of Light, to Stormhaven where they received the assignment from Lakmir to infiltrate Shadowgate and prevent the warlock arising the Behemoth. There were many tricks and traps that mostly relied on trial and error, puzzle-solving, as well as good combative skills.
Eventually, the Cosmos warriors made it to the warlock's stronghold only to fight the Behemoth itself. Everyone failed as it was too powerful, though Firion was revived. He was the only warrior who assembled the sacred Staff of the Ages which, as heeded by Lakmir, was the key to seal and defeat the Behemoth. Empowered by Cosmos' portions of her powers to every fallen warrior, via the orbs found and the Crystals earned in Dissidia, both foes fell into the abyss! Thanks to Terra, Cecil, and Prishe, the large party teleported as the Castle was collapsing never to be seen again.