foldworks<p>A blue door with a coal hole cover in front of it, Lancaster, England</p><p>I’ve walked past these coal hole covers for over 20 years without realising what they were <a href="https://en.wikipedia.org/wiki/Coal_hole" rel="nofollow noopener" translate="no" target="_blank"><span class="invisible">https://</span><span class="">en.wikipedia.org/wiki/Coal_hole</span><span class="invisible"></span></a> </p><p>To be fair, they're next to squarish covers labelled "Water" and even the roads nearby don't have coal holes</p><p><a href="https://mathstodon.xyz/tags/DoorsDay" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>DoorsDay</span></a> <a href="https://mathstodon.xyz/tags/DoorThursday" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>DoorThursday</span></a> <a href="https://mathstodon.xyz/tags/Door" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>Door</span></a> <a href="https://mathstodon.xyz/tags/CoalHoleCover" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>CoalHoleCover</span></a> <a href="https://mathstodon.xyz/tags/CoalHole" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>CoalHole</span></a> <a href="https://mathstodon.xyz/tags/opercula" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>opercula</span></a> <a href="https://mathstodon.xyz/tags/StreetFurniture" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>StreetFurniture</span></a> <a href="https://mathstodon.xyz/tags/ManholeCovers" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>ManholeCovers</span></a> <a href="https://mathstodon.xyz/tags/photography" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>photography</span></a> <a href="https://mathstodon.xyz/tags/design" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>design</span></a> <a href="https://mathstodon.xyz/tags/history" class="mention hashtag" rel="nofollow noopener" target="_blank">#<span>history</span></a></p>