The road from Moscow to Yakutsk in Siberia is interesting to say the least. Even though it is a Federal Highway, most of it is unpaved and becomes either impassable or lots of fun, depending on your outlook and the vehicle you're driving.
Actually, it's sometimes very dangerous when it's raining. After one storm, over 600 vehicles were stranded. Many people ran out of fuel and got very hungry. Mobs were breaking into vehicles to search for warm clothing and food. Construction teams were beaten by people who had been stuck for days.
If they can get past these problems, it looks as if mud fanatics would have a great time, just about every time it rained!