I once became obsessed with following the Shibuya River as far as I could through central Tokyo. It's hard to explain the fascination, as the river is merely a concrete channel — little more than an ugly drain — and is mostly built over. But that was the key to my interest: The idea that there was an almost-secret river flowing through and under this most urban of Japanese cityscapes. I wanted to explore it.

The waterway probably gave the area — now the youth mecca of the metropolis — its name. The phrase commonly used to describe it in the olden days — "shibu-iro no kawa (iron-ore-colored river)" — combines with the character for valley ("ya") and results in Shibuya.

Anyone who knows the route of the river will know that it flows under the mighty edifice of Shibuya Station — and it was there where my quest was thwarted. I balked at the idea of disappearing alone into the Tokyo underworld. With my video camera I went a little way in, finding on the broadening river banks signs of subterranean human life: mainly beer cans and the wrappings of food snacks. Very quickly the light disappeared — and there were rats. I'd seen them even in daylight around the famous statue of the loyal dog Hachiko outside the station, and if they weren't scared of running around in daylight above ground, how much more confident would they be in their home, their nerve center?