Mysore's Railway Museum is a compact open-air collection of locomotives, coaches, and railway equipment close to the city's station. It is especially good if you are curious about how rail travel shaped southern India beyond the romance of the palace and markets.
The highlight is the mix of heavy machinery and old carriages, including pieces linked to princely-era travel. It is an easy add-on between central sights, and families usually get more out of it than the modest scale suggests.