Koh Rong is the largest island off Sihanoukville and one of the most beautiful in southeast Asia. About 45 minutes by speedboat from Serendipity Pier, it has a long arc of white sand at the main village (Koh Touch), plus a string of quieter beaches reached by jungle trails or longtail boat.
The island is steadily developing — small resorts have replaced some of the original bungalow camps — but much of the interior remains forested and the further-flung beaches still feel remote. Sok San on the west coast is a six-kilometre stretch of sand with almost nothing on it. Bioluminescent plankton in the bay at night is a routine highlight on the swim tours.