I read the Romney, Hythe and Dymchurch Railway is an impressive 13+1⁄2-mile (21.7 km), 15 in (381 mm) gauge light railway.
There was a local egg ranch that had a 7.5" gauge setup. Us kids could have a ride if our parents bought eggs. My grandmother's brother-in-law built a good sized steam engine, perhaps a 4-6-2 loco or even larger. (I wonder where it is now?) Gosh, that was a _long_ time ago, but it seeded my interest in riding scale railroading.
Building in that size forces one to do real engineering on bridges and everything else. I always wanted to do something in that size, but couldn't even afford the smaller 7.5" size.