🇹🇭Thailand

Thailand is one of the world's easiest warm-water countries to plan around scuba, freediving, and snorkeling because it has two very different coasts. The Andaman Sea side (Phuket, Krabi, Khao Lak, Koh Lanta, Koh Lipe) delivers the classic offshore marine-park experience, with the Similan and Surin island groups running seasonally and offering the country's best big-reef scenery. The Gulf of Thailand side (Koh Tao, Koh Samui, Koh Phangan, Chumphon) is the training and repeat-diving workhorse: calm bays, short boat rides, and a huge course ecosystem.

The trick is timing. West-coast conditions peak in the drier window, while the Gulf often stays workable through different months. Build your trip around the best coast for your dates, then use Thailand's fast domestic flights and ferries to connect. Add a few non-dive days for limestone cliffs, night markets, and island viewpoints, and you have a high-reward trip for mixed groups.