I recently went to Kyushu for a bike trip, and tried to find the 'Nabeyama no Yu' spring mentioned on this site. I made one wrong turn, and ended up finding a different one (Hebi no Yu) instead. While I never did find Nabeyama no yu, some people I met at this second one, Hebi no Yu, said that they liked the second one better.
Hebi no Yu was only about a 1 minute walk from the gravel road / parking, had 4 different temperature tubs (each larger than Nabeyama no Yu's), a changing hut and a toilet hut up by the parking. The hot tub was bearable, but not for a long time, and the two medium temperature tubs were ideal. The one other tub was good for beginning or cooling down in. The tubs are located beside a stream, which is also nice to cool off in. Also, at the top of the trail down to the springs, there is a perfect location to camp, complete with a firepit.
A map with a descriptions and directions to this location is here:
http://www.communitywalk.com/map/5751#101335WM3:8f10733.1;Y48131.1Zcm
and it will soon have pictures, once I get them off of my camera.
-Ben