Koh Tan Coral Reefs and Snorkeling at Koh Madsum from Koh Samui

Koh Madsum, also spelled Koh Matsum, is a small island in the Samui Archipelago. Koh Madsum and the larger neighboring island Koh Taen are located just a few-minutes boat ride from the south coast of Koh Samui. Koh Madsum and Koh Taen belong like Koh Phangan or Koh Tao to the Samui Archipelago (Mu Koh Samui), which consists of about 69 islands. On the contrary to the Ang Thong National Marine Park, which is almost advertised everywhere, there are not many visitors on Koh Madsum.

Ko Samui (or Koh Samui, also often locally shortened to Samui) is an island off the east coast of Thailand. Geographically in the Chumphon Archipelago, it is part of Surat Thani Province, though as of 2012, Ko Samui was granted municipal status and thus is now locally self-governing. Ko Samui is Thailand's second largest island after Phuket.

Ko Taen (or Koh Tan) is an island, approximately 15 kilometers off the mainland and 5 kilometers south of Koh Samui in the Gulf of Thailand. It is part of the Samui archipelago (Mu Koh Samu), which includes about 60 other islands. Just northwest of Koh Tan is the Mu Ko Ang Thong National Park. The island is accessible only by boat. The island has several beaches suitable for snorkeling. The island is surrounded by coral reefs, which survived and partly recovered from the widespread dynamite fishing in the region until the 1980s. Many small bungalows have been built on Koh Tan, especially since in the late 1990s, of which some can still be rented by small groups, but many of these businesses have given up. There are paths that are interesting for mountain bikers. Koh Tan features a large mangrove forest on the southwest coast with abundant wildlife. Monitor lizards can be seen during a walk through Koh Tan quite often. There is still a small temple in Koh Tan with a freshwater spring right on the beach.