These photos are quite amazing but the most striking are the ones that reveal the scale of what is being shown. Seeing a 10-story flight of stairs or people in the context of these tunnels transforms them, revealing how massive they truly are. It’s impossible to know how large these objects are without a frame of reference. But by putting something familiar into these scenes, the photographer has provided us with a sense of scale that is extremely powerful.

Photos of Japanese storm water drainage system (via Digg).