I have a hill block. I intend to build a tunnel from the middle of the slope to the large basement of the workshop on the top of the hill. About 100 feet. I know it sounds nuts but it would be really cool. Who has a tunnel? I kind of want an underground pool too so I can feel like Gene Hackman as Lex Luthor.
The problem with underground is the mustiness. Basement and tunnel would be atop a drainage plane and moisture barrier, with walls and tunnel ceiling having a moisture barrier and ventilation plenum. Pumps and fans governed by sensors.