Ban Thung Pho Junction is the point the southern line has a small branch down to Khiri Rat Nikhom.
Originally, the branch down to Khiri Rat Nikhom was meant to go all the way to Phuket. But construction stopped in 1956, and it seems to no longer be a priority. Not many tourists head that way. While taking the train will get you half way to Khao Sok National Park, which is gorgeous, you’re still going to have to go the rest of the way by road.