Particularly big right now in London, "explorer-artists" meeting in subterranean passages to share their experiences in drain and train infrastructure, abandoned silos and other "off Limits" infrastructure around the world.
I made contact with Australian Cave Clan founder Doug who, in addition to sharing some very claustrophobia-inducing stormwater drain experiences with me, organized for other Clan members to send me some incredible photos of Australian drains and tunnels. Here are shots of down under Down Under, Australia as you will never see it in the postcards!