[from
here]
The change was immediate, like walking into the refrigerator: the air was cool and damp, the rumbling in the last room had given way to silence, and Indy couldn't see a damn thing. Experimentally, he held his flashlight out in front of him and moved it toward his face; the light barely penetrated through the fog.
A careful step forward told him the ground was solid, at least here, but nothing about what else might be in the room. He turned back to try the door (let some of the fog dissipate into the other room), but it was locked and wouldn't give. With no way to burn off the fog, all they could do was keep going--cautiously. "Stick close," he said to the others: his go-to maxim in situations like these.