Nam Tok Phaeng is protected by a national park and is a pleasant reward after a short but rough hike. After the waterfall (dry out of season), it's a further exhilarating 15-minute climb up a root-choked path (along the Phaeng-Domsila Nature Trail) to the superb Domsila Viewpoint. The two- to three-hour trail then loops through the jungle past other waterfalls where the eagle-eyed might spot wild boars, snakes, deer and monkeys.
It's possible to continue up to Khao Ra, the highest mountain on the island at 625m. If you do consider this, go with a guide as it is very easy to lose one’s way. Whichever trek you do, tell someone your plans before you set off and take water, appropriate shoes and a sun hat.