If you want to see the most dramatic sections of the Thai-Burma Railway, then you might want to consider riding the line from Kanchanaburi to the end of the line at Nam Tok. This makes a nice "DIY" day trip. There are four trains a day to Nam tok and back. The most convenient train leaves the station at the Kwai Yai Bridge at 10:50, reaches Nam Tok at 12:50 and returns to Kanchanaburi about 15:00. The one-way far is 100 Baht (2.60 USD) but there's also a 'special' car for 300 Baht (7.79 USD). It's still a third class carriage, but they've added some cushions to the old wooden seats and also provide some snacks and drinks. I'm not sure it's worth it, but the stewards were friendly, pointing out some sights along the way, and the price tag insured that the car wasn't crowded.