"The walls really go all the way along the mountains?" said Justin.

"Why is it, Master Holmes, that you never believe anything I have to say?" said Zechariah, busy saddling the steeds.

Justin shrugged. "It's just hard to imagine, that's all."

Sheer faces rose straight up. The walls looked too natural to be manmade yet too perfect to be natural. Nearby, a massive stairway carved into the wall led all the way up to the top, but it had been worn so smooth by the hand of ...