Between 1859 and 1964 this narrow-gauge railway hauled coal and passengers between Merthyr and Brecon. A 5.5-mile section of track, between Pant Station and Torpantau at the head of Pontsticill Reservoir, has been restored and steam locomotives operate on the line. The trip takes 65 minutes with a 20-minute stop at Pontsticill (you can stay longer if you like and return on a later train). Check the timetable online.
Pant Station is 3.5 miles north of Merthyr bus station; take bus 35 (20 minutes, departs every 15 minutes, hourly on Sunday) to the Pant Cemetery stop.