The first rock he put his foot on shifted, almost sending him sprawling. He grunted and continued, half crawling, with his injured arm pressed to his chest. When he had made it to the summit of the rockpile, he reached out and grabbed the barbed wire. It was jammed in tight; he had to tug hard several times to get it out.

The daylight barely made it past the opening. He could see the tunnel floor, a channel of brown, stagnant water. The tiny white limestone stalactites hanging from the ceiling. Further in, darkness. Solid, like matter.

As he crawled across the rubble on his belly, his body blocked the light; for a few moments, he could see nothing. But as soon as he started sliding down the slope, the tunnel became visible once more. He crawled down and got to his feet.

He stood stock-still, listening. The mouse sitting in front of him was listening as well. It gingerly poked the stuffy air with its nose and whiskers. Then it pattered off. It ran in a straight line, like a tightrope-walker. Suddenly it stopped and sat back on its hind legs. Apparently, that was as far as it would go, at least by itself, because it turned back and looked at him.

His nostrils flared, but the only thing he could smell was wet concrete and stagnant, subterranean air. Rusting iron.

He strapped on his headlamp and switched it on.

Further on, the tunnel turned sharply and in the wavering beam of the headlamp he could see the water ripple away from his feet and lap against the walls.

There was a door to the right. A small room. Some kind of rack on the walls. Bent iron pipes that looked deep-fried in rust.

He splashed on down the tunnel, led by the mouse, and after rounding the corner, he stopped. There was something there. He turned his head to catch it. A whiff of rot. He moved his head this way and that, sniffing, testing the air from different angles. Rotten meat.

A few paces further in, he stepped over a high threshold, entering a cave. Glassy bumps protruded from the rough cave walls. When the light hit the drops of water hanging from the ceiling, they twinkled like constellations.

Something lay on the floor in the middle of the room. He went up to it. A backpack. There was a water bottle in the mesh side pocket. A small stuffed moose with a rounded muzzle dangled from a string. He studied the backpack and the ridiculous moose for a long while.

He let the beam of light from his headlamp sweep across the uneven walls, but there was nothing to see. Except a staircase.