The system is made of a central tunnel and several smaller side tunnels.

Then they were sucked into a side tunnel, an outlet.

Caught a look at a man going into one of the side tunnels.

They came to the fork where the side tunnel led off into the rock.

But I've wandered down a side tunnel, as the saying goes.

An instant later he had turned into the side tunnel, and none too soon.

That's why I had it made in a side tunnel far away from us.

The first guard was at the entrance to the side tunnel.

You might also note the side tunnel beyond the bodies.

Then there was a flash of light, up a side tunnel.