This is the story of Russia's Lena Highway, aka the Highway from Hell.  Russian federal highway Moscow city - Yakutsk City looks very modern when you start you journey from Moscow. But thousands of miles later, between the cities Ukhta and Naryan-Mar it just doesn't look like a road anymore.

As you can readily see for yourself from the pictures, in the summertime, the Lena Highway turns completely to mud whenever it rains.   There are several Internet sites that consider the Lena Highway to be the worst road in the world.

Source: 1, 2