Avalon

History

Avalon was salvaged from parts of Cable's ship Graymalkin.  X-Force deceptively destroyed Graymalkin after S.H.I.E.L.D. attempted to invade it and use it for their own purposes, but most of its critical parts remained cloaked or within X-Force's possession.

The mutant messiah Magneto later acquired several parts, eventually building the mutant sanctuary Avalon, a haven for mutants that floated in space.  The base became headquarters to Magneto's group the Acolytes, including high ranking member Exodus.  While Exodus tried to recruit Magneto's former students from the New Mutants (who were now part of the Cable-led militant group X-Force) to stay in Avalon, Cable returned to his former ship and tried to destroy it.

Unfortunately, the ship was later destroyed when Onslaught attacked the base leading to it crash landing into unknown parts of Australia.  Many members of the Acolytes died, but several--including Exodus, Scanner, Frenzy, the Kleinstock brothers, and Unuscione--were able to survive.

Ironically, Avalon's parts once again came into the possession of Cable, who used the remnants of Avalon to build his isolated island nation Providence. 
 

Alternate Realities 

 
Earth 295: Age of apocalypse   

In this reality, Avalon was the last refuge of Humans and Mutants who wanted to escape Apocalypse´s tyranny.  The place was a real paradise full of life where humans and mutants coexisted in peace and harmony.  The placed was ruled by Destiny and Cypher (her adoptive son).
 
It was located hidden at the Antarctica, ressembled Savage Land of main reality but with different topography, this site was one of the only places in earth free from interference of Apocalypse until Shadow King mindcontrolled every inhabitant making them kill each other and burn the villages. Thus it was abandoned.
 
In order to reach the Sanctuary, people must get passage from the tribe Ghost Dance in the "Infernal Gallop", then Mystique ferried refugees from an Antarctic station to the shores of Avalon. Then  the travelers would be conduced into Avalon by Cain (a massive monk).