The main Souunkyou waterfall is pretty fantastic. Tons of tourists get off a big bus and take pictures of it. If you prefer a smaller waterfall in the middle of the forest with almost no other tourists, that this place is for you.
You will need to park close to the closed down hospital at the top of the main Souunkyo hotel area. The walk to the waterfall will take around 20 minutes through a densely forested trail.
The below Google map is an approximate location of this waterfall.
open Google map