This post is from last year. I figured I'd post it again since the weather has been so cold this year that the Jyväsjärvi skating track is already open and waiting for you to get out and try out your skating skills. According to the Kotakahvila blog, the cafe won't be open until the 6th of January, although since I haven't been down there to check things out this year, I'm not sure if this information is correct or not.
After a long wait the ice skating track is open on Lake Jyväsjärvi. It is most conveniently accessed from the harbor area. I'm not exactly sure but I would guess that the track is at least a few kilometers long if you skate the full loop. There is also a cross country ski track that follows along next to the skating track.
The Kotakahvila offers hot beverages as well as kicksled rentals. According to the sign, the sleds rent for 5€/hour.