As far as Tony could tell, this was the only entrance to the tunnels (existing, and that would not, possibly, compromise their structural integrity. He would, after all, not be landing at all, never mind exploring the structure if he had no care for causing harm where he did not want to. Those patches of heat, that was). From here, they didn't look much like any kind of freaky, psycho testing facility he was expecting. But then, it wouldn't be a very good secret if it was obvious. He only hesitated a moment longer in the derelict power house, giving it one last glance over his shoulder, then left it to the pigeons.
The tunnels were not saved from the vandalism that had covered the power house itself. The rusted pipes that ran along the walls, unused but still damp at their fastenings and the rot eating away at the metal, were covered in graffiti and etchings of the poorest proclamations of love and vomit of jealous hate, hidden where no one would find or disturb them. Iron Man ignored them, flicking through different views to keep on course as he ducked through the narrow passages; strict blue magnetic resonance; nebulous yellow thermal.
"Store database i-g-a-slash-inact-slash-nine-oh-five-five run, pull flyover data from i-g-a-slash-atten-slash-two-two-two-six and compare, and don't just run it and shut it down this time, JARVIS, I need to use my own eyes, too--" Tony was muttering, trying to keep his thoughts organized, only to have them halted by the end of the line. That was, a pile of dirt and concrete, the roof of the tunnel caved in. Flick, blue, flick, yellow, that wasn't fooling anybody.
The explosion sent dust falling from the ceiling all up the tunnel and back in the power house, sending the birds into their hysterical flapping once more.