I left my hiding place too soon. I didn't know exactly when sunrise would be, or even if that's what controls the lives of the things that live down here. I'll have to be more careful in future: I almost ran into one of the creatures.
It was standing by a metal bin in which something was burning. That was what saved me. I smelled the smoke and saw the glow before I was close enough to see the creature. I crept over to look, ready to run at the first sign of movement in my direction.
I saw the creature in silhouette. It was roughly humanoid, though the head was misshapen and too big, and the limbs looked out of proportion. It was standing next to a pile of mechanical parts, bending over to examine them, putting some back and throwing others on the fire. I watched it for a while, unable even to guess what it was doing. In the end, I forced myself to leave and found a hiding place. I waited there for an hour. I didn't hear the creature come past, but when I went back, the fire was extinguished and the creature was gone. There were no more parts on the floor, but there were still some in the ashes of the fire.
I walked deeper into the tunnels.