Had noticed on a display board outside Bangkok main railway station that railways in Thailand, or rather Siam back in the day, started off as standard gauge but were regauged to metre gauge.
A visit to the site of the "real" Bridge on the River Kwai is a must for those of an enthusiast persuasion, a few Glasgow-built steam locos, loco and truck/railcar of Japanese origin (a reminder of WW2) and a Garratt were on display.
There's a small well-hidden railway museum in Bangkok itself. And at Bangkok Noi there's a depot (with a few steam locos in residence for runs up to Kanchanaburi). Thai rail staff don't have a problem with giving foreign devils permission to have a wander around. Not much H & S in evidence.