Trans Mongolian Railway

It’s fab. I loved it and will do it again

If it’s a long-distance rail-travel record you’re after, begin your journey from Thessaloniki (or Athens) in Greece, cross the east Europe to Moscow, take the Trans-Mongolian route from there to Beijing and continue to Hanoi and then to Ho Chi Minh (Saigon) in Vietnam!
Then you can cross the Cambodia borders to Phnom Penh by bus and then continue your trip by train till to Singapure crossing two other countries, Thailand & Malaysia – a journey of 18,000km. I did that and it was amazing!