>>41262924
The Sealed Gate is the gate to the esper world.
https://finalfantasy.fandom.com/wiki/Esper_(Final_Fantasy_VI)
Espers were created as a result of humans coming into contact with magic and the Warring Triad during their war for dominance. The gods realized that what they were doing was wrong and sealed themselves away in the forms of statues. They gave the espers back their free will and asked to be protected by them. A second war began between espers and humans seeking to use their powers, beginning the War of the Magi. At the height of the war, the espers created a new realm, where they escaped with the Warring Triad's statues.
A handful of espers remained in the world, such as Valigarmanda, who was frozen in ice, and Odin, who was petrified in the Ancient Castle buried deep within the mountains. Ramuh lived in the human world for an unspecified time, using his humanoid appearance to blend into normal society, and he implies that other espers did the same. The espers' magicite remains also remained, such as Ragnarok and Phoenix. As the remaining espers concealed their existence, the knowledge of magic became the stuff of legends and myths.