From the Author: "In my research for this book, I looked at dozens or hundreds of drawings and photos from tunneling operations in the 1800s. I was blown away by the skills and knowledge of those people! What we even find hard to accomplish today, they did with no electricity, no diesel engines, nothing - just hard work and ingenuity. These images had a huge impact on the final story, as you've seen. This is why research is one of my favorite parts of writing - I get to learn so many cool new things!"