Much like conditions out at Round Lake, the Trout Creek Wildlife Refuge is in amazing shape for fat biking. It doesn't get quite as much use as Round, but plenty of snowshoers, xc skiers and fatties have packed in some nice single track loops and out and backs. And there have not been many walkers. Sorry, there is no map for the area. There are 2 park entrances, I prefer the Rapid Lightening side. Plus the Pack River store makes for a great post ride refreshment and food stop.
Take your camera as there is a good chance of seeing wildlife...mostly birds. And don't fret about getting lost. Most of the refuge is open, and it is pretty easy to see where you are going and where you have been. So, be adventurous. One warning though, the trail that goes up the hill on the backside, and sidehills over to the Trout Creek Rd is fairly long, has some good climbs and doesn't get as much use as the trails down on the delta. It can be a tough haul.
Refuge is free to use.