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.
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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.
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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.