When you're in Noboribetsu, make sure to check out the Oyunuma Pond!

Noboribetsu features a remnant of an active volcanic crater---Oyunuma Pond, which is a hot spring marsh emitting the smell of sulfur every day, located just behind the Hell Valley of Noboribetsu Onsen. Entering from the entrance of Hell Valley, you can soon see Oyunuma Pond. Walking along the Oyunuma Pond trail for about 20 minutes, you'll reach the Oyunuma Pond Lookout, where you can view the entire landscape of the pond. Following the downhill trail, it takes only five minutes to reach the Oyunuma Pond area. There are fewer visitors to Oyunuma Pond compared to Hell Valley, and the smell of sulfur is quite strong. It's not advisable to stay too long in this area, but it's okay to linger for a while when it's windy. The active volcano surrounding Oyunuma Pond has an elevation of only 366 meters and is still an active volcano that occasionally emits white smoke from its summit. According to local folklore, fishermen in the past would predict the weather at sea based on the direction of the wind blowing the smoke from the summit and the amount of thick clouds, which is a very interesting piece of knowledge.