As already stated there are two operations on Kauai.
The newer tourist operation is called
Kauai Plantation Railway
The older is the
Grove Farm Homestead & Sugar Plantation ("Grove Farm museum"). This museum is located primarily at the original headquarters of the plantation. It has the historic locomotives from the sugar plantation and operates them occasionally. It is proposing to develop a train ride using the steam locomotives at a location near the heritage site. Information can be found on its website. The original Grove Farm operation is now devoted to land management on Kauai; its ownership changed back in 2000.
Early this year I took a 15-day cruise to Hawaii and had reserved the tour going to both locations. But, we had heavy rains that morning and threats of flash flooding so roads were closed and the bus tour did not operate for safety reasons.
Brian Norden