Koča pri Jezeru and planina Voje are great in summer time, but I think that at the moment it would be quite difficult to get there because of frozen snow. I have to say, that I am not a fan of riding bike in winter time. There is much more to do in other sports (snowboarding, skiing, cross country skiing, ....), but I think you can also find something ridable for your bike in Bohinj or in Slovene language (bi se dal kej najdt)

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Also adding pictures (unfortunately from mobilephone) Koča pri Jezeru.