1. Ang Thong National Marine Park
What is is? One of Thailand's most mesmerising marine reserves, laced with limestone islands, coral reefs and secret beaches.
Why go? While you'll find some colourful snorkelling spots around Koh Samui, Ang Thong Marine Park offers a veritable kaleidoscope of aqua-based action. Book a full day trip (including lunch) with a reputable tour operator such as 100 Degrees East, whose shiny white speedboats come with kayaks, trained snorkelling guides and are limited to just 12 guests.