It's amazing just how much stuff there is under Tokyo - not just infrastructure like this and the usual transport links but entire multi-storey shopping malls. There's almost a whole city beneath the city. It's possible to travel for miles without ever seeing daylight!
Even just the transportation infrastructure is incredible to me. I was just there and it was honestly amazing to me how deep the metro stations can be. Multiple long escalators/stairways from surface to platform.
