The stair went down for a long time.
It turned four more times after the landing, and at every turn the channel on the left-hand wall turned with them and went on, and the red inside it kept going at the speed of a man walking.
The air changed on the way down. The stale mineral cold of the upper corridor gave way to something wetter — the walls were damp to the touch by the second turn and running by the fourth, and the whole stairwell smelled of old mortar and standing water and something underneath both that James did not have a word for.
Their footsteps came back off the walls at two and three seconds and did not agree with each other.
And somewhere well below them, a long way off, something made a noise.
It was not close. It was not aimed at them. It was the sound of a large thing in a large space, arriving through a lot of stone, and it happened twice on the way down and then did not happen again.
"That's fine," said Cillian. "I've decided that's fine."
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