Consider Kanotoiwa in Hinohara village, Tokyo. This is a cascade running between an enormous rock split in the middle (Kanotoiwa means Divine Gate Rock) . There is a cottage and campsite nearby, and also a number of waterfalls in the vicinity you can visit by bus or hike.
This is the HP for the cottage/campsite Nagataya
http://homepage2.nifty.com/nagataya/index.html (sorry no English)
You can email them (the bottom left button below the phograph) or call their Tokyo office at 03-3391-0275.
Here are some pictures of the place I found on the internet.