presumably a S.H.I.E.L.D. base
It is the greatest creation to come from the mind of Mister Fantastic, but it is perhaps the deadliest weapon in the history of science. The Cosmic Cube can bend reality with just a thought from whoever is in contact with it. It would be dangerous even in the hands of those who mean well, but in the possession of someone as cruel and evil as the Red Skull the results would be disastrous.
After the catastrophic events Magneto unleashed upon the world, resulting in the deaths of several heroes, A.I.M raided the Baxter Building and stole the blueprints for the Cosmic Cube. The recently reformed Ultimates sent Captain America and Hawkeye to retrieve them, but they were bested by the Red Skull. A.I.M. might have been the only other organization intelligent enough to build the cube.
Once completed, the Red Skull took control of the cube and a newly formed Black Ops team under the leadership of Nick Fury was dispatched to eliminate the threat. These Ultimates were no match for the Red Skull while in possession of the Cosmic cube, but Captain America found a way to fatally wound the Skull so he could do no more harm, and S.H.I.E.L.D. could recover the cube.