Mobius Archive

The Mobius Archive is a dimension out of space and time of everything else. it has one entry/exit point - a wormhole in space that appears every 23 days for 5 days.
The wormhole always appeared in the orbit of Orebim, home of the outer-rim dwarves. The dwarves were highly distrustful of the enigma and it was often a sore-spot in their vision of sovereign control over tier planet and immediate orbit.
At one time an order known as the Order of the Hidden Sun maintained space-station / monastery, called The Gloridon, that was positioned where the wormhole appeared.
The order and the station furthered the dwarves ire, but all efforts to drive the order away failed as the order possessed "time cannons" that could send attacking vessels forward in time by an unknown number of weeks.
The order was on good terms with the "Archivists" (Sphinx) who dwelt within the archive. The order served as a sort of "clearinghouse"/gatekeeper for items and issues brought to the enigma. A great many items and issues did not pertain to the Ancients , but the ones that did got their full attention. Artifacts and relics to dangerous to this world and relating to the Ancients were usually inducted into the archive for proper care and/or oversight.
Demonic Invasion The status quo changed when elements within the Order of the Hidden Sun became corrupted by demonic influence which set the stage for an epic event. As a Demon Orb was brought to the Archive, the Demon within (Vugyargis saw an opportunity to elevate himself to god status.
A relic was used to neutralize the Sphinxes in the archive while hordes of demons arrived by a demonic vessel known as the Agradotha. The demons swept the station of the order - staged to take control of the Archive. The demon possessed leader of the order delivered the Demon Orb to the Archive, a process that released the Demon Vuguargis for what would have been its destruction by the sphinxes. with the Sphinxes incapacitated, Vugyargis was able to enter the vault of the gods and attempt to ascend to a place among the pantheon.
After the Agradotha collided with an locked onto the Gloridon, the dwarves raced to the fight seeing an opportunity to rid their space of the demons and the order.
Fortunately, some heroic PCs managed to engage and defeat Vugyargis during his ascension. Because Vugyargis "new home plane" was the Mobius Archive (a requirement of his ascension), his death was also his destruction. The dwarves (and a few un-corrupted members of the order) defeated the demons.
The Gloridon and the Agradotha were bombarded into oblivion by the Dwarven space navy. When the PCs emerged from the fight with Vugyargis, nothing was left of either structure.
Aftermath
The Archivists invited the Dwarves to engage in diplomacy who accepted and re-engage in discussions every 23 days when the archive reappears (anything left within when the wormhole closes, can never return).

The Mobius Archive as depicted in an ancient tapestry.