[jasonbvr]

Christmas in Japan is mostly a holiday for couples. You will be hard pressed to find anywhere "festive" outside of a shopping district.

That being said, Christmas skiing or snowboarding is excellent since most Japanese people are working that day.

If that is not your thing and you still intend on going to Nagano, check out Matsumoto castle which should have a nice layering of snow on it by then. After that head up to Nozawa Onsen to relax in a hot bath. There is a special winter festival in Nozawa but no idea when it is.

Nikko in the winter should be fantastic. Nikko has huge old growth forests and is littered with temples. All of which would be quite picturesque frosted with a bit of snow. Then head up the mountain to another little town that ends in Onsen for yet another steamy hot bath.