I read it some months ago, it's very good. He makes a point of not speculating much, though he doesn't rule out anything, and he backs up everything with references to documentation he's collected over the years through library research or FOIA requests. Published in the late 90's.
Here's another:
Underground Bases and Tunnels: What is the Government trying to hide? by Richard Sauder Ph.D.
I read it some months ago, it's very good. He makes a point of not speculating much, though he doesn't rule out anything, and he backs up everything with references to documentation he's collected over the years through library research or FOIA requests. Published in the late 90's.
https://eventhorizonchronicle.blogspot.com/?m=1
Dr. Sauder's blog.