Drains...

These guys explore drainage systems in Canada! And some nice photos and words come out of it all.

"The built environment of the city has always been incomplete, by omission and necessity, and will remain so. Despite the visions of futurists, the work of our planners and cement-layers thankfully remains a fractured and discontinuous whole, an urban field riven with internal margins, pockmarked by decay, underlaid with secret waterways." - http://vanishingpoint.ca/about.html

Thankfully indeed! Add it to your list of hobbies to take up.