The Death Railway in Kanchanaburi, Thailand
Recently I was reading about the "death railway" between Thailand and Myanmar. The Siam-Burma railway was really dangerous to construct and was dubbed the death railway after people died in the construction.
There is a train that runs on weekends that stops in a few locations where you can jump out and have a look around for an hour before moving on to the next place.
I bought the 240 baht air conditioning seat which is really good for a really long journey. Non air conditioning seats have windows you can lean out of to take photos but I couldn't sit in a noisy train for so long. The train left central Bangkok at 6:30 AM and then I got out at Bang Sue station on the way home at 19:00.