A ferry ride from Koh Samui, Koh Tao, otherwise known as Turtle Island, is world-renowned for scuba diving and an excellent place to learn or enhance your skills as there are so many dive shops. Sail Rock (technically between Koh Tao and Koh Phangan) is widely considered one of the best dive sites in all of Thailand for its secret (but not-so-secret) pinnacle, which rises about 15m above water and extends 40m deep to offer a haven of marine life for divers of all levels.

These two small, unspoiled islands, an hour from Koh Lanta are part of Mu Loh Lanta Marine National Park and offer an abundance and diversity of marine life (with great turtle-spotting), some of the most pristine coral reefs in Thailand, and pretty beaches. Good for all levels.

On the outer fringes of Mu Koh Lanta Marine Park and a three-hour trip from Koh Ngai, these famed diving sites are musts for experienced divers. Hin Daeng, known as Red Rock, and Hin Muang, known as Purple Rock, feature amazing color in the coral and anemones, steep walls, huge shoals of fish, whale and nurse sharks, tuna, barracuda, and more. Nearby Koh Ha (between Hin Daeng and Phi Phi) offers stunning caverns with stalactites and is a great spot for a night dive.

Snorkeling or diving around Koh Phi Phi’s limestone cliffs is bucket-list stuff while in Thailand. Dive with leopard sharks at Shark Point, considered the best dive site at Koh Phi Phi while Lana Bay, and the Mosquito and Bamboo Islands offer rich and shallow coral reefs for snorkelers.

A haven for divers and those looking to get their PADI certification, Koh Chang is home to one of Thailand’s largest shipwrecks, the HTMS Chang, making for an unforgettable diving experience. There are several rock pinnacles like Hin Luk Bat and Hin Rap where you can see the world’s biggest fish, the whale shark. If you’re looking to snorkel, make your way to Pearl Beach. Nearby islands like Koh Wai offer relatively undisturbed islands and uncrowded dive sites with shallow, hard coral reef populated with stingrays, leopard sharks, and colorful reef fish.

Aptly named Coral Island for its plentiful coral reefs, you’ll find beautiful beaches and harmless tawny nurse sharks and blue spotted stingrays swimming just offshore. Head to Nual “Monkey” Beach for some more secluded snorkeling or any beach on the western part of the island for soft and hard corals.

One of Thailand’s few privately-owned islands, snorkelers and divers off the pristine beaches at Koh Talu can see broad swaths of colorful fish thanks to the island’s resident fish conservationist. Diving trips to nearby islands can also be arranged. The island’s one resort has beachside bungalows, private beaches, snorkeling, and diving opportunities. Guests can seed new coral in the reefs and contribute to sea turtle preservation efforts.

This quiet island is off-the-beaten tourist track and known for its off-the-beach snorkeling. Enter the water in front of Ao Niang Resort and swim to a significant drop-off (that runs from the southern cape to the National Park headquarters) to find colorful corals and massive schools of fish.

This group of nine islands with crystal clear waters and a sea turtle sanctuary are protected national parks and only reachable by boat from November to April. Book a day tour or stay overnight at Pakarang Beach to snorkel islands four to nine from February on to see manta rays and whale sharks.

Located near the Thailand/Malaysia border, this small, southern island is a tropical paradise for divers, with what is considered one of the best-preserved seabeds, with exceptional underwater fauna. Get your PADI Open Water certificate on the island to explore famed diving spots like Sting Ray City, Yong Hua Shipwreck, Stonehenge, Boonsung Wreck, Hin Takorn Dukong, and 8 Mile Rock. For those more interesting in snorkeling, rent a mask and walk straight into the water off any of the island’s main beaches like Sunset Beach and Pattaya.