Koh Bon is an unique island compared with the Similan and Surin Islands. Both the Similans and Surin are comprised of huge granite boulders. Koh Bon is formed by sedimented limestone. Referred to as the middle island by the Thais, Koh Bon sits alone 23km northeast of the Similan Islands. Koh Bon was added to the Similan Islands Marine National Park in 1998.
Like the Similans, Koh Bon is surrounded by the clear, turquoise waters of the Andaman Sea. However the limestone rock gives the island a very different feel. In the bay to the southwest side of Koh Bon it is clear to see the different layers of limestone laid down over thousands of years. The rock is dark and imposing. The dense rainforest of the Similans is replaced by scrub grass and wind swept trees that cling to the rocky top of Koh Bon. Although it is not possible to go ashore at Koh Bon, there is still plenty of wildlife to spot from the boat. Sea eagles soar overhead and herons skim over the top of the water. The dramatic change in scenery at Koh Bon is also apparent when you go snorkeling. The stunning limestone continues down to the depths underwater. The tropical fish life is the same as the Similans. What makes Koh Bon so special though is at certain times of the year it is possible to spot the graceful Giant manta ray (Manta Birostris).