I had a wonderful time cycling along the walking paths during the Spring. Even though I didn't get a chance to visit any of the local onsens, the scenery alone was worth the trip. The lake is incredibly beautiful, calm, and peaceful—a perfect escape.
It's a very interesting and unique place to visit. You'll see geysers and smell sulfur in the air. There's a trail to walk around the entire crater. There's a spot for visitors to dip our feet in the hot/warm water too. A good half day can be spent there. It gets warm so I suggest visiting in the early morning.
Beautiful area, cable car was fun. The bears in their mountaintop park was entertaining. The Ainu huts was educational and an extra bonus was a large 4 point deer lounging about 20 yards from us.
Noboribetsu Hell Valley is formed on the rim of an active volcano, so you'll see smoke rising and smell a kind of sulfurous odor (it smells almost like rotten eggs, so be aware). I visited in early winter, so the valley was covered in white snow, creating a truly magnificent scene!
Absolutely stunning volcanic park complete with geysers and sulphur in the air. Do yourself a favor and go further in than just the observation deck at the entrance. There are a number of low intensity hikes to do here.
More about Shikotsu-Toya National Park from our blog