Koh Samet, Rayong

Bangkok’s quickest island fix sits off Rayong, a straight shot by highway, then a short speedboat from Ban Phe pier. White-sand bays stack along the east coast, from party-leaning Sai Kaew to mellow Ao Wai. May often brings sun in the morning, a short storm late in the day, then a pink sunset. You can split days between snorkel spots, beach strolls, and grilled seafood right on the sand. Resorts line many coves, yet you still find quiet corners south of Ao Phrao. Ferries and boats run often, and you can be on the beach by lunch if you leave at first light. Pack a light rain shell and reef-safe sunscreen, and keep cash for park fees at the pier.