Richard Sauder, PhD
4 Star The original overview from 1995 first serious book about deep underground military bases (DUMB)
Although Amazon lists this book as published in 2014, that is a reprint date. This is the original 1995 publication, and the author, a PhD who does not drink or do drugs, is the original open source intelligence investigator of a trillion dollar plus secret program that is off the books — neither authorized by Congress, nor the funds declared to Congress.
While the book is a quick read, it represents years of work by the author, and includes explicit detail including diagrams, locations, names, and more. It also includes photographs and explanations of tunneling capabilities used to create underground cities that could be as many as 20 levels and miles below the surface of the earth.
Also covered is magnetic levitation pneumatic technology that makes possible very long distance travel, underground, in short times.
There is a bow toward extraterrestrial possibilities but these are not documented as well as the facilities and tunneling are.
The author is careful to distinguish between what he knows and what he is speculating might be true. I myself have doubts about the extent of all of these things, but in the past two years I have been persuaded that trillions of dollars have been spent on a secret space program (also not authorized by Congress) and secret underground capabilities.