The Gwili Railway is a heritage line just north of Carmarthen, using preserved steam and diesel trains on a rural stretch of track through the Gwili valley. It is a gentle outing, especially good if you are travelling with children or have any affection for old railways.
Check the timetable before going, because the experience depends entirely on operating days and special events. When trains are running, it makes a relaxed half-day contrast to Carmarthen's castle, market, and older town centre.