Deadly Trap: Abyss Protocol

From the introduction:

Under the dust and gravel and detritus of a bygone age is a door in the ground. Once uncovered, its only seal is a large handwheel caked in rust. It takes quite a bit of force to get the wheel turning but once it starts, it remembers its purpose. The seal breaks with a dry hiss as stale, recycled air escapes. On fist-thick hinges, the door’s pneumatics push the steel shield up, revealing a single, hazard-yellow ladder leading into the earth, its paint barely dulled by time. Huge thuds shake the ground around the hole as work lights flash to life, illuminating the descent.