According to Official Guinness Records,
The world's longest run without changing trains is one of 10,214 km (6,346 miles) from Moscow, Russia to Pyongyang in North Korea. One train a week makes the journey by this route, which includes sections of the famous Trans-Siberian line. It is scheduled to take 7 days 20 hours 25 minutes.
For a complete list of 1900 records, please visit 1900 Guinness Records in Russia.