North of the Similans lies Koh Bon, Koh Tachai, the Surin Islands, and Richelieu Rock. All of these areas offer world-class diving that differs from the Similans and should be part of your itinerary when you visit the area.
Koh Bon: The Perforated Island
Koh Bon is located about 20 kilometres north of island #9 and features one of the only vertical walls in Thailand. The dive site is on the southwestern point and consists of a 33 metre wall facing the small cove, and a step-down ridge that carries on to depths of over 45 metres. Leopard sharks are common on the ridge and on the sandy flats below the wall.
Although the soft corals are not as high-profile as they are in the Similans, the colours of the corals are radically different and include shades of turquoise, yellow and blue, besides the more common pinks and purples. Koh Bon is one of the better places to see manta rays, especially towards the end of the season when there is more plankton in the water.
Twenty-five kilometres north of Koh Bon, Koh Tachai has an offshore underwater ridge that runs perpendicular to the island. This is considered to be one of the finest dives in the Kingdom and is famous as a place to see not only the more common species of corals, fans and tropical fish, but larger animals such as rays, leopard sharks, nurse sharks and hawks bill turtles.
Whale sharks make an appearance on a regular basis. Tachai also boasts a breathtaking sandy beach on its northeastern shore; a great place to hang out and feel like Robinson Crusoe.