Book excerpt: In Subterranean Twin Cities, geologist, historian, and urban speleologist Greg Brick takes us on an adventurous, educational, and-thankfully-sanitary journey beneath the streets and into the myriad tunnels, caves, and industrial spaces that make up the Twin Cities' fascinating and surprisingly vast underground landscape. In this groundbreaking tour, the first of its kind of the Twin Cities, Brick mines the stories that lie below the city surface.