Crowley doesn't feel things the way that Aziraphale feels them. He feels shifts in energy, he smells the sulfur on the heels of other fiends from the pit. He smells the stinkingly sweet aroma when an angel is present (as opposed to the pleasant earthly musk Aziraphale has taken on). He can feel when there is a strong celestial energy approaching or when there is attention on him, but he lacks the empathic nature that Aziraphale has honed his skills on, and so all he feels inside of the stone walls are the Thing that he's sure Aziraphale keeps mentioning.

"Nor have I." he replies, almost whispering, every step he takes more careful than the last.