I love taking trains to save money and going low and slow you get to see more of the country.
I did Saigon to Nha Trang on a overnight sleeper.
Bangkok to Malaysia on a sleeper. The next time I am going to go all the way to Singapore!
But the longest and the most fun was......
Xian to Lhasa Tibet took 36 hours and climbed to over 5000 meters. The train averaged about 90 KM an hour on the Tibet plain, not sure how many miles that was.