Similan Islands, Koh Bon, Koh Tachai and Richelieu Rock, Thailand
The 9 Similan islands lie off the cost of Thailand in the Andaman sea. They are part of a national park which also includes the islands of Koh Bon and Koh Tachai. Further north lies Richelieu Rock, part of the Surin national park. It is often claimed that the region offers the best diving in Thailand.

What to see:
Similans: The east side is sloping with sand, some boulders and coral. The west side which is more often dived offers a special ambiance with giant granite boulders, soft coral, arches and especially at the site „elephant head rock“ many swim-throughs. Ribbon as well as giant moray eels, bluespotted sting-rays and sometimes big fish like white tips or napoleon wrasses can be encountered
Koh Bon and Koh Tachai: Mantas if lucky and sometimes leopard or white tip sharks, wall and ridge covered in small soft corals and seafans, huge amounts of glass fish and bigger schooling fish hunting in the early and late hours of the day, octopus, moray eels, some nudibranchs. Schooling barracudas and sometimes whale sharks at Koh Tachai
Richelieu Rock: Big diversity of marine life, loads and loads of different fish around the rock including some bigger fish like barracuda and trevalli. Cuttlefish, octopi, large groupers, some macro like ornate ghostpipefish, tigertail seahorses, cowries, frogfish and harlequin shrimp. If lucky whale sharks or mantas can be encountered at this submerged pinnacle which is often claimed to be the best dive site in Thailand. Soft and hard coral, seafans and anemones.

Loads of awesome photos from the area here.

Level: From entry-level if doing the advanced course during the trip, strong currents, most dive sites are fairly deep, diving on nitrox is recommended

How to get there: Flight to Phuket, public bus, minibus (THB 600 / USD 17) or taxi to Khao Lak (around 1 hour, THB 1200-1500 / USD 33-40), Khao Lak offers a wide variety of hotels and hostels

Water temperature: 29-30°C with thermoclines (also called the green monster) down to 26°C

Visitbility: 20-40 m

Season: November till May, the park is closed during monsoon season

Price: Liveaboard from Khao Lak (from THB 20’000 / USD 560 for a 3 night trip with 11 dives to THB 80’000 / USD 2300 for a 6 night trip with over 20 dives), daytrips from Khao Lak for around THB 5000 / USD 140 for two dives, it takes around 2 hours to reach the dive sites by speed boat

My trip: I flew to Phuket and had the hotel organizing the transfer. I did dive with Khao Lak Scuba Adventures on a 4 night liveaboard with Manta Queen 3 which costs THB 23’000 / USD 640. The fleet has 6 boats on 3 to 5 night trips to choose from. The boats are basic but offer all you need on a short liveaboard. Mainly young travelers make the trips on the manta queens a lot of fun. The staff was awesome and our experienced guide Anja found all the cool stuff for us.