Russian Airspace
Getting a clearance through Russian Airspace can be very tricky. A lot of military airspace. In my case my crew and I were ferrying a turboprop airliner from the USA to Japan and needed to stop in Russia for fuel. We had planned to fly the aircraft from Los Angeles via Anchorage and then directly west but due to airspace restrictions had to head up to Nome Alaska and then south west to Magadan for fuel before continuing onto Japan. Minimum flight level was above 20,000ft. You will definitely need special visa's to fly into Russian Airspace. We also discovered that they used a lot of metric figures for weather, altitude etc. This was nearly 20 years ago. We were in Russian controlled airspace all the way and all the Russian aircraft at our level and above were talking in their own language. Yet the controller we had enjoyed practicing his English when communicating to us. It took me several weeks before we departed for me to study the jep charts and possible alternates. My suggestion is that you carry at least two GPS systems because if you go off track then there is a chance of military interception. Good luck but be very careful and do study the airspace and checkout the price of fuel well in advance.