Image from the Complex Osówka, part of underground town build by Nazi Germany during the project Riese. The complex is located near the villages of Kolce and Sierpnica, inside Osówka Mountain, now in Poland
<a href="//commons.wikimedia.org/wiki/User:Chmee2" title="User:Chmee2">Chmee2</a>
CC BY-SA 3.0
<span class="int-own-work" lang="en">Own work</span>