Worth checking out is a massive post detailing photographer Phill Davison's recent exploration of the half-collapsing tunnels and overgrown hillside entrances of an old Yorkshire iron mine.
Right when you think it's over, they hike out through snow drifts and cross into another walled-up creek entrance—and the post just keeps on going. 
Davison remarks at one point that the structures he finds himself surrounded by down there remind him of smugglers' caves and shipwrecks—and pictures like this one, below, detailing the awesomely compressed strata of wood boards and rock, and the rusting ironwork that holds it all back from collapse, make that comparison viscerally obvious. 
How amazing, though, to descend into the earth only to find it kitted-out like the hull of an oceangoing ship. Where the hills you're walking on are actually engineered archways of an earlier civilization, with the occasional entryway peeking out from beneath the weeds. And so you descend into the vaults and debris-support cages of an artificial interior, hidden behind fences and beneath the winter snow.
Check out Davison's post in its entirety—and then stop by the Flickr pool "Exploring the Megastructure," where I originally saw these photos.
