Rainbow Falls is a steep climb from Dongbu Hot Springs. If you look closely you can see a little red bridge and a different waterfall almost directly above Dongbu Hot Springs. I did not see a rainbow at 11am in the winter so I will have to return sometime.
The hike: It is not a long hike but it is all uphill. The hike follows a steep road that passes several restaurants along the way.
How to get there: Take highway 21 from the north or south to Dongbu Road. It will be a short drive to Dongbu Hot Springs crossing the new Dongbu bridge. There is parking throughout Dongbu Hot Springs but I parked at the big visitor parking lot next to the green suspension bridge. I think all roads going up in Dongbu Hot Springs eventually end at the Rainbow Falls trail. I walked past the school and police station on my hike.
Other info: No entrance fee.
GPS data: waterfall: N23.56671 E120.93702