City of Siegen (Westphalia, Germany): Blocked entrance of the mining adit <i>Hainer Stollen</i>, located in the east side of the <i>Siegberg</i> mountain. During late WWII, this centuries-old iron ore mine was specially prepared in a secret operation of the national socialist regime. In 1944, it was used to host important cultural artifacts and pieces of art of Westphalian churches and museums as a protection from air raid damage. Among these items were the Aachen Cathedral Treasury <i>(Aachener Domschatz)</i> and the casket with the remains of Charlemagne <i>(Karlsschrein)</i>. In April 1945, the treasury in the adit was detected by U.S. troops who returned the items to their original places in May 1945.
<a href="//commons.wikimedia.org/wiki/User:Frank_Behnsen" title="User:Frank Behnsen">Frank Behnsen</a>
CC BY 3.0
<span class="int-own-work" lang="en">Own work</span>