Koh Racha Yai

Koh Racha Yai sits around 20 km south of Phuket in the Andaman Sea, a 30-90 minute boat ride from Chalong or Rawai pier depending on the boat. There’s no national park fee here — a real difference from Phi Phi or the Similans — so the only cost is whatever the day-trip operator or resort charges. Most people come for a few hours of snorkelling; a small handful of resorts mean you can also stay the night.

Patok Bay, also called Ao Tawan Tok, is where the day boats land: a sheltered, U-shaped stretch of white sand on the west coast with an easy coral reef a short swim from shore. Walk about 200 metres over the low hill to the north and you reach Siam Bay, longer and quieter, with one beachside restaurant and fewer anchored boats. Three smaller coves on the east side — Lha Bay, Ter Bay, and Kon Kare Bay — see almost no day-trip traffic at all, reachable mainly by resort longtail or a walked trail. Snorkellers find coral gardens with parrotfish and the occasional reef shark in the shallows; certified divers head slightly deeper for moray eels and better visibility on the fringing reef.

November to April is the calm-water window, with the best visibility for both snorkelling and diving and the smoothest crossing from Phuket. The island doesn’t shut down for the May-October monsoon the way the Similans do — swell builds on the exposed west-facing bays, but boats keep running to the sheltered east coast, so a rainy-season visit is still workable if you’re flexible about which beach you swim off.

Insider Tip: Day-tour boats cluster at Patok Bay between roughly 11am and 2pm for the lunch stop. Book an overnight room instead of a day trip and you get the beach mostly to yourself once the last boat pulls out around 4pm.

Watch out: High-season midday (Nov-Apr) brings a lot of boats to Patok Bay at once — walk to Siam Bay or one of the east-coast coves if you want space to swim without dodging traffic.

For a second Andaman island day trip from the same piers, Coral Island (Koh Hae) is closer and calmer for beginners; divers wanting bigger fish and fewer beaches should look at neighbouring Koh Racha Noi, a short crossing further south.