Numappara Walking Area
This is a nice area for walking in Spring/Summer. Its part of the whole Nasu walking trail network so you could easily walk in from Nasu too.
There are picnic tables at the parking area. For a short walk you can just walk around the ponds there. Its kind of a flat marshland area. Its quite unique and beautiful.
Then there are a lot of longer walks you can do from there too. Please note the monkey in the above shot. There is even a hot spring not too far away that we have not investigated yet.
Finding the turnoff can be a bit tricky. I'd suggest you closely study the google map linked above. If you zoom in you can see the kanji for the lake and adjacent green area. They are signposted from the turnoff on route 266 but not easy to see and even our Japanese friends missed it twice.
I'd like to hear from people who have walked extensively in this area. Seems like there are lots of possibilities.
See also Sandogoya Onsen