WARNING: The following article contains spoilers for Justice League #69, on sale now from DC Comics.
One of the most recognizably iconic locations in the entire DC Universe is the Fortress of Solitude, the longtime personal headquarters of Superman. Serving as both the Kryptonian's home away from home and an advanced base of operations, the Fortress of Solitude is one of the most impregnable facilities in the DCU, housing incredibly powerful secrets and cutting edge alien technology. As the Justice League is called to deal with crises all over the globe, Superman is shocked to discover that the Fortress of Solitude has been whisked away from right under his nose.
Teaming up with the reformed clandestine organization Checkmate, the Justice League combats forces linked to the villainous Leviathan around the world. In addition to fiery threats in Los Angeles, the heroes face false versions of some of their greatest enemies who were hired by a mysterious benefactor to serve as distractions to the League. As the two teams regroup to contemplate the purpose behind this strange series of attacks, Superman's trusty robot Kelex surprises everyone by revealing that the Fortress of Solitude has been stolen in Justice League #69 (by Brian Michael Bendis, Phil Hester, Eric Gapstur, Hi-Fi and Josh Reed).
The exact circumstances of the Fortress' disappearance are still unknown but all that remains in the arctic locale where the headquarters was situated is reducing to nothing but a swirling sea, with Kryptonian crystalline pylons seen haphazardly protruding from the water. Given that the Fortress of Solitude normally contains an entire bestiary of extraterrestrial creatures, the Phantom Zone projector and a wealth of Kryptonian technology, recovering this stolen headquarters has become a priority for the heroes. Unfortunately, not even Batman, the World's Greatest Detective, seems to know where to start.
The Fortress of Solitude's location is something of an open secret in the DCU and has been targeted repeatedly in the past, across a variety of mediums. In the 2006 film Superman Returns, Lex Luthor infiltrate the Fortress in an effort to steal technology that he could use to build his own kryptonite-laced land mass. In the comics, Mongul famously infiltrated the Fortress to subjugate Superman with a mind-controlling plant known as the Black Mercy, and in the more recent crossover event "Endless Winter," the villainous Frost King is revealed to be imprisoned beneath the Fortress, emerging empowered by the Kryptonian technology within.
The Justice League learned that their old enemies, the Royal Flush Gang, had recently upped their game and ambitious reach and the Fortress of Solitude, with all its advancements and secrets, would make the ultimate heist.
How exactly any supervillain could make off with such a majestic, mighty installation is perhaps an even bigger mystery than the identity of the culprit responsible, but regardless, Superman is currently without his longtime headquarters. And with the Fortress of Solitude gone, other superhero headquarters like the Batcave and Hall of Justice could be next on the mysterious thief's list of high-profile targets.