I had no idea Marlin was known for that. My in-laws live in Robinson and we used to pass through Marlin when coming up from Houston, so all I ever really saw was what is visible from Highway 6. Very interesting.
Found this interesting and amusing from an article on texasescapes.com.
"A hot artesian spring was struck by accident in 1893 and the town became known for its curative waters. This was the era of health awareness (people became aware of how little they had) and what better excuse was there for leaving home, than "taking the cure" in Marlin? Even today you can drink from a fountain from that era, right next to the Chamber of Commerce Office. You can soak your feet too, and they've thoughtfully provided a separate facility for that purpose. Water has a tendancy to purge and locals have timed it's effects at 43 minutes"