You can ride fatbikes on the cross-country skiing tracks, and there are also other alternatives.
Please read the FATiquette rules and plan and behave accordingly.

Geilo Husky groom tracks that are nice to cycle on. They are easy to find between Vestlia Resort and the lake or between Mailatunet (the grey buildings) and Solli.

The Husky track leads from their base-camp over the lower part of the lake and onto the upper part.
Later in the season the tracks from another dogsled company meets the Geilo Husky trail on the far end of the lake. This makes it possible to ride back on the north shore of the lake towards Geilo Beach. 
Important: If you use the husky tracks you need to give way to the dogs if and when they arrive. Please make space for them to pass, move out the tracks and into the loose snow when you see a dogsled approach.

During some parts of the season we groom some fat bike/ multi-use trails right outside Vestlia Resort with a Snowdog or snowshoes. 
These are somewhat more narrow single-tracks that demand some balance and bike-handling skills. In other words, good fun!
Those trails meet the Husky trail.
After heavy snowfall or due to strong winds these trails might not be suitable for fat biking.