Lots of nice hotels at Toya and it is right beside an active volcano that last blew up in 2000. There's a part of the town that got heaved up around 70m during those eruptions. You can walk through the ruins, areas that were houses and roads are now craters and a cracked landscape with sulphorous fumaroles. Obviously the onsens here are genuinely naturally hot!
The lake itself is really beautiful with islands in the middle that can be accessed by a ferry. On Mt Uzu there is a ropeway from which you get great views of the lake and back down on Showa Shinzan, a smaller volanic peak that grew out of a farmers field during WWII. You also get a view on the other side out over the Sea of Japan. All in all a spectacular region. I spend a lot of time there in summer camping. The lake also has a whole heap sculptures around it which are pretty cool.
Here's some pics
From the ropeway looking back over the lake in winter
Looking back down to Showa Shinzan
A nice shrine at the lake edge
Awesome place for camping in the few warmer months we get up here
