An emergency exit in the <i>Charonne's tunnel</i> on the old <a href="https://en.wikipedia.org/wiki/chemin_de_fer_de_Petite_Ceinture" class="extiw" title="en:chemin de fer de Petite Ceinture">chemin de fer de Petite Ceinture</a> (French for "little belt railway") in Paris, France.
<a href="//commons.wikimedia.org/wiki/User:0x010C" title="User:0x010C">0x010C</a>
CC BY-SA 4.0
<span class="int-own-work" lang="en">Own work</span>