Amazing underworld river system in Tokyo

 "[Tokyo] is a geologically challenging place to build a megacity - a flat floodplain of soft, alluvial soil, in a monsoonal climate with frequent typhoons, on active earthquake and volcanic belt."

This is not too far from the underground cavern.
I've no idea of how far it extends.

"Few capital cities have been shaped by water as much as Tokyo. Its densely populated suburbs are criss-crossed by rivers and canals."

I saw a video video this week that gives an unusual glimpse of Tokyo, the place I've lived for eight of the last nine years. another part of this network of underground caverns has been built near where we live. We ride over it at least once a week, you wouldn't know it was there.