The exact location of The Pluto Vault (also referred to as 'The Plutonian Vault' or simply 'The Vault') is entirely unknown. The dwarf planet Pluto is merely suspected to house the station. Due to the militarization of the dwarf planet, no-fly zones have prevented current maps to be made of the surface for slightly less than 7000 years. The most current map is the one made by the Draconis survey ship back in 2891.
Towards the end of the Second Age, the URSS was severely weathered by countless wars. Desperate, the URSS began to increase weapons development ten-fold to assist the war effort. Suspicions circulated that the URSS had removed laws preventing the development of overly inhumane weapons in order to help the war effort. The URSS denied these claims, stating them as "preposterous" and "unpatriotic.".
At the very end of the second age, the URSS signed the Confederacy of Humanity, resigning leaderships of the star system Sol to a government represented by the surrounding planets. Several years after the signing, Pluto, previously a small, desolate world, was cordoned off, allowing large scale construction upon the surface. When questioned about the nature of the establishments, the government stated it was a "prime source of water-ice," and the construction was of a "fuel depot for future settlements,"
During the second age and the URSS's dramatic increase in weapon technologies, rumors soon spread that laws preventing the construction of inhumane or torturous weapons had been temporarily removed, permitting biochemical warfare, advanced nuclear weapons, and weaponized planetary collisions, even permitting the removal of atmospheres from planets. Those of this belief failed to produce any evidence for or against the theory. Soon after, the public's focus was directed towards the signing of The Confederacy of Humanity, and the thought was largely, although not entirely forgotten.
Several years later, the topic returned when the system began to construct instillations on the surface of the planet. Some theorized that, to strengthen trust between worlds, the plans for the now highly controversial plans were hidden in some form of underground bunker to prevent trial from exterior governments. There is no known evidence that supports this theory.
Today, the Pluto Vault is it's own form of myth. The secrecy of the location of the Vault has intrigued many people to the point where it is used in common language today, usually to express eccentricity or strangeness, usually in a humorous fashion.