Underground Pits at Kamensk

The  were underground areas that existed at the Kamensk military base prior to the 0.57 update.

General
There were once four total pits at this base, but only the three pictured below were ever accessible. The fourth remains in the southeast corner, but it still cannot be accessed. The other three are gone indefinitely.

Trivia

 * These accessible pits were in the game from 0.50 until 0.56, and in 0.57 they were removed entirely.