The "Rainbow Spring"at the Rainbow Resort is officially named the "No.1 Jhihben Geothermal Well". Drilling egun on November 14 1982, by the CPC company and was completed on January 26 1983. The well is 1460m deep with a diameter of 8.5". The wellhead temperature is 135℃, with a daily output of 400 tonnes at a pressure that sends the waters up to 8 stories into the air. The pH value is 8.71 and it is classified as an alkaline sodium hydrogen carbonate spring (NaHCO3).

As the "No.1 Jhihben Geothermal Well" is located right inside the "Rainbow Hall" at the resort, you can enjoy the high quality waters of what is truly "Jhihben's No.1 Hot Spring" in your own suite, with open-air spa baths and indoor hydrotherapy pools.