Occasionally, either WMDs or magical artifacts are made that are too powerful and dangerous for the world on which they originated. The denizens of those worlds or the powers that be entreat angelic beings to lock such threats away, trusting they will thereafter not fall into the wrong hands. The massive treasure store of this world thus contains many magical and technological items of great power and danger.
These objects are actively guarded at all times by angels. Not merely divine messengers or saintly servants, the angels have adopted the technologies of other races to upgrade both their extraplanar peace-keeping forces and their garrison here. Thus seeing an angel protected with a suit of matter-phasing armor and wielding a combat rifle is not uncommon. Each angel also has a comm unit to coordinate with others in the event of a breach.
The great hall itself is built nearly like a temple. While its exterior is massive, it is bigger on the inside than on the outside. In order to get to where the artifacts are stored, one must pass through no fewer than seven halls on seven garrisoned floors.
Even if some unscrupulous thief or dungeon-delver were to somehow bypass those defenses, the lower vaults are filled with traps and mazes to prevent access. While the tunnel walls and twisting passages of the cavern are an impediment to would-be robbers, the angels’ armor allows them to phase through solid matter, including walls, to immediately intercept and apprehend them upon activation of the alarms. In the seven million years this multiverse guardhouse has stood, only two items have ever been stolen, and never from past the 3rd vault floor.
(I do not own the images in the above collage, and all copyrights belong to their respective owners.)
Go to another world …