On the other side of the tunnel, we see sunlight. Though we are underground, there is a hole at the top of the cavern that is open to the sky. I think it’s called an oculus. Someone flying overhead would be able to see the city without much difficulty, but from the outside, it probably looks like a mountain.

“At least we have another way out,” I say, not really thinking about the amount of climbing it would take to get out of here.

There’s a waterfall that flows from the ...