Tenkai Fortress

The Tenkai Fortress (Japanese: 天界の要塞, Tenkai no Yōsai) is a legendary and mysterious place, located on Quarton. It has been told to have great powers inside of it. The Corrupted and the Corekai are looking for it. The Corrupted found the location first. The Knights and the Corekai fight the Corrupted to take control of the Fortress. Its currently unknown of how to break the seal.

In the Series
It was first mentioned in "No "I" in Team" by Granox, then by Mr. White, where he was explaining to the boys about it and they must find it before Vilius does.

In "Hang Tenkai", Vilius, Granox, and a War Stallion were at the outside of the cave of the Fortress. Vilius says it is the Tenkai Fortress and he used its energy to shapeshift the War Stallion into the Ice Rhino. Later, the Knights and the Corekai attack the Corrupted. Bravenwolf uses Elemental Titan Mode to destroy many Corrupted soldiers and combines his powers with the Volt Jet to create the Flame Phoenix and used it to defeat Granox and the Ice Rhino. Vilius decides to retreat and the Knights ask Beag if he and the Corekai can guard the Fortress, which he says he will.

In "Fortress Revealed", the Knights and Beag walk into the cave of the Tenkai Fortress. They tried to break through the barrier, but failed. Later, Tributon combines his elemental powers with the BlasTank to create the Ice Walker and used it to defeat Slyger, the Fire Raptor, and Sky Griffins from taking control of the Fortress.

In "Looking Forward, Looking Back", the boys and Mr. White watched past battles to think of a solution to open the seal to the Tenkai Fortress.