London

"A moving city!" she said, stopping short. "I -- I mean he -- he meant to move London.... The thing in the vault, it's an engine, isn't it?" She remembered the designs she had seen in the notebook at Kit Solent's place. She remembered drawing them now. Just doodles, they had been; the first inklings of an idea. "An external combustion engine, based on an Ancient device called a Stirling engine, but far more efficient ..."

Fever Crumb, Chapter 35, Memories, pg 200/232