He heard a bubbling, hissing sound, such as a dragon or Worm might make, but followed it, and the air-current, along a slowly descending tunnel until he came to water's edge. Knocking off a few sparks from his flint and steel he saw that the air he'd been following this whole time was boiling up out of a subterranean lake that filled the tunnel before him and completely blocked his way out. Having nothing else to do, he sat down to die, and fell asleep instead, and had nightmares that were an improvement on reality.