The Grand doors of Evercrest are massive 20ft tall adimantium doors, shieded by powerfull abujration magics. Each door is Chromatically locked, requiering certan color coded keys to unlock. While all doors are closed that are within the vault of eternity the whole fortress is benefitting from these same effects: Each door blocks teleportation trough it, blocks magic that alters it's form or that allow creatures to walk trough it. The magic also extend to the Etherial plane.
When the right key or keys are placed upon the door, its surface temporaly become liquid around the spot, allowing the keys to enter the door.