Donggang Stream Waterfall (中文版: 東港溪瀑布) group has one very tall and beautiful waterfall on a side stream and a smallish but secluded waterfall in the main stream. There is a rope you can climb to continue up the river, although I've never gone. Since I've never been passed the first waterfall, I can only assume that what's up there is possibly the most spectacular waterfall that anyone has ever seen.
The hike is less than 10 minutes to the side waterfall, and less than 10 minutes from there to the next one. This river completely dries up in the winter and early spring, so the best time to go is from the first hard spring rain of typhoon until January.
Donggang Stream Waterfall is very close to Dongxi Waterfall, so you should try to visit that one in the same day.
Donggang Stream Waterfall
Pingtung County, Taiwu Township
Waterfall: 22.57196, 120.6423
Parking: 22.57426, 120.63976
Detailed Map: https://goo.gl/Sbr9xa