Stalin's bunker situated 60 m underground is still one of those objects which simply do not exist officially. So, if you happen to be in the basement of one of the "Stalin-era" buildings and see a sign "Admission by order", know that behind that door you will find a bunker.
Unfortunately, nowadays these legendary Soviet constructions are being relegated to oblivion... So, after opening a few hermetic doors, you will see a staircase and an elevator shaft. Mind that the way to the bunker is not simple and will take you a while.