Deteriorated concrete on the underside of a stairway in the <a href="https://en.wikipedia.org/wiki/New_York_City_Subway" class="extiw" title="en:New York City Subway">en:New York City Subway</a>.
<a href="//commons.wikimedia.org/wiki/User:B137" title="User:B137">B137</a>
<span class="int-own-work" lang="en">Own work</span>