The Crossing storyline introduced us to one of Tony Stark's best-kept secrets: his rolling fortress of solitude.

High atop the world, nestled into the frozen landscape of the arctic, hidden beneath many feet of snow, lay Stark's secret bunker. A large, heavily fortified and heavily armed, fully automated facility, the bunker was also a luxurious get-away.

Immense on the exterior, it obviously had a roomy interior. In fact, the cold bunker was warm and welcoming on the inside, a sort of high-tech ski lodge. Besides a holo-theater and quarters, the bunker featured a fully stocked gourmet kitchen.

The fortress featured a full lab contingent with manufacturing equipment. It also housed a backup Armory of dozens of Iron Man armors, including several exotic and previously unseen models. (Iron Man could come and go from the base via a port located in the ceiling.)

Despite being in such a remote locale, the bunker featured maximum security. A perimeter alarm triggered automatic defense measures. Intruders deemed a threat to the bunker could be dealt with harshly by the system, which had in its arsenal sensor-driven laser cannons, among other things. To enter it's massive steel doors, a person would need to pass through four levels of security: (1) a password ("Mallory"); (2) a voice print analyzer on that password; (3) a retinal scan; and (4) a palm-print scan. Defense measures could be monitored and controlled from the Defense Command Center in the heart of the bunker.

But the real surprise of the bunker was that it wasn't a fixed base. In reality, it was a giant mobile armored attack vehicle, that cruised along on tank treads. When the need arose, the juggernaut could be deployed in a tactical way, rolling over opponents if need be.