I took the two photos above from the road and kept driving in search of parking to get a better look.
I ended up parking about 800 meters down the road in front of a trail map. There was what looked like a very overgrown road that kind of matched up with the trail map. The map showed a 1.2 kilometer hike down to the river, but I couldn't figure it out. It may have been over my skill level of hiking, or it wasn't really the right trail.
I went home and researched it more. Apparently, there was a typhoon that came through the area in 2004 and destroyed Ikoi no Hiroba and they have been working to restore it ever since there. There was a sign pointing down to the river and that it was a 10 minute hike. I think that sign was posted pre-typhoon because there was no trail there.