Than Sadet is the most historically significant waterfall on Koh Phangan, set in a national park covering the island's northeastern interior. The waterfall cascades over a series of smooth rock shelves before meeting the Than Sadet River, which flows to a quiet beach on the east coast. The park entrance fee is 100 baht.
The trail from the park entrance to the waterfall takes around 45 minutes through dense jungle. The falls are best in the wet season (June to October) when the flow is strongest. The beach at the river mouth — Than Sadet Beach — is undeveloped and peaceful, with longtail boats available for return trips to other beaches. The park also includes the Khao Ra viewpoint, accessible by a longer and steeper trail, which offers the best panoramic views on the island.