This is a part of one of two main tunnels of the "Government Bunker Germany", near Marienthal, Ahrtal, Germany.
NATO mandated Germany to provide for a fallback of the government to strike back a nuclear attack. You can visit the last 203m of formerly 17km full equipped bunker. So did I, and it felt a bit depressing and childhood memories of low-flying and siren drills increased.
... you should not know ... by pcpanik