After WWII the Eastern part of Germany became occupied by the Russian troops known as "Gruppe der Sowjetischen Streitkräfte in Deutschland" (GSSD or Группа советских войск в Германии). This is one of their 777 (!) military complexes and so well protected and preserved it just makes you want to scream "Ich bin ein Urbexer!!".
After the German unification the place became abandoned as the last Sowjet soldiers left in 1994.