There are a number of ice-skating venues that pop up across Japan during the winter months, but the vast majority of those are man-made structures typically located in urban areas. If you're wanting to skate in a more natural setting, the Kera-ike Skating Rink in Nagano is formed by a frozen pond in the forest adjacent to the Karuizawa Wild Bird Sanctuary – and it's every bit as beautiful as it sounds.
Another reason why this rink might appeal to people is that unlike smaller, urban rinks, you can skate freely rather than being bound to a clockwise or counter-clockwise only setup.
If you're visiting with children who aren't quite at independent skating level yet, they've also got "Little Bear Chairs" for hire which have a seatbelt for safety purposes.
The prices for skating are 1900 JPY for adults (junior high school students and older), and 1300 JPY for elementary school students and under. Please bring a knit cap and gloves for skating – if you don't have them, they're available to purchase at the venue.