Siaes Tunnel is a massive underwater cavern that offers a unique deep diving experience in Palau. Divers descend to 30 meters to enter the tunnel, which is decorated with sea fans, and can see sharks and rays silhouetted against the bright blue exit.

The small island of Siladen, next to Bunaken, is fringed with some of the most beautiful and pristine hard coral reefs in the marine park. The shallow, sunlit reefs and calm conditions make it a paradise for snorkelers and beginner divers.

Silfra offers a diving experience you can't get anywhere else on Earth: swimming between the North American and Eurasian tectonic plates. The water is glacial melt filtered through volcanic rock for decades, resulting in over 100 meters of visibility.

The Silver Bank is a submerged coral bank north of the Dominican Republic that is a crucial breeding and calving ground for North Atlantic humpback whales. For a few months each year, liveaboards take snorkelers here for incredible, respectful, in-water encounters.

The Silver Bank is a submerged coral bank north of the Dominican Republic that is a crucial breeding and calving ground for North Atlantic humpback whales. For a few months each year, liveaboards take snorkelers here for incredible, respectful, in-water encounters.

Silver Banks is a large, pristine coral reef at Cocos Island. It's a fantastic spot to see the incredible biodiversity of the island, with a huge variety of fish, eels, and a large population of whitetip reef sharks.

Silver Banks is a large, pristine coral reef at Cocos Island. It's a fantastic spot to see the incredible biodiversity of the island, with a huge variety of fish, eels, and a large population of whitetip reef sharks.

Silver Banks is a large, pristine coral reef at Cocos Island. It's a fantastic spot to see the incredible biodiversity of the island, with a huge variety of fish, eels, and a large population of whitetip reef sharks.

The Silver Star is a deep wreck for advanced divers. This former fishing vessel lies at the bottom of a steep drop-off, and its deep, exposed location makes it a great spot for seeing larger pelagic fish like tuna and barracuda.

The Similan Islands are a protected national park in the Andaman Sea, known for their stunning underwater landscapes formed by giant granite boulders. These create dramatic swim-throughs and channels, and the white sandy bottoms are a great place to spot leopard sharks.

Simon's Wreck is a large, purpose-sunk pinisi (traditional Indonesian boat) that lies in deep water off Gili Meno. It's an interesting wreck for advanced divers, now covered in coral and home to schools of fish and large groupers.

The mystical island of Siquijor offers beautiful, uncrowded diving. The island is surrounded by a protected marine sanctuary with healthy reefs, beautiful walls, and a high diversity of fish life, all in a very relaxed atmosphere.

Sister Rocks are a series of volcanic pinnacles that offer a fun and varied dive. The site features numerous swim-throughs and overhangs, and is a great place to see turtles and nurse sharks resting.

The Skalaheim is a small Chinese freighter that was sunk as an artificial reef. It sits in shallow water and is a very easy and fun wreck dive, perfect for beginners and for a second dive of the day.

The Skerries are a group of rocky islets off the coast of Anglesey, Wales. They are home to a large colony of grey seals, offering fantastic and playful encounters. The surrounding waters also have beautiful kelp forests and numerous shipwrecks.

Skomer is a protected marine reserve and a major seabird colony, famous for its thousands of puffins. Underwater, it offers some of the best diving in the UK, with incredibly rich invertebrate life, particularly a huge diversity of colorful nudibranchs.

The Skudesnes is a smaller, shallower wreck in Gulen that is perfect for recreational divers. The wreck sits upright and is a beautiful artificial reef, covered in colorful anemones and home to a variety of fish.

Small Giftun is a famous drift dive in the Giftun National Park. The site features a spectacular wall covered in a forest of huge gorgonian sea fans, and it's one of the best places in Hurghada to see the large and impressive Napoleon wrasse.

The SMS Brummer was a fast minelaying cruiser. The wreck lies on its starboard side and is incredibly well-preserved, often with excellent visibility. It's a beautiful and very photogenic wreck, a favorite among many Scapa divers.

The SMS Cöln is a light cruiser and one of the most intact and beautiful wrecks in Scapa Flow. It lies on its starboard side, and its guns, bridge, and other features are still clearly visible, making it a favorite for photographers.

The SMS Dresden is another of the fantastic German light cruiser wrecks. Lying on its side, it is very well-preserved, with its armored conning tower and deck guns still in place, making for a spectacular advanced wreck dive.

The SMS Kronprinz Wilhelm was a massive German battleship from WWI. The wreck lies on its side, and its huge, 12-inch gun turrets are an awe-inspiring sight. This is one of the most impressive and historic wreck dives at Scapa Flow.

The SMS Markgraf is another König-class battleship and one of the deepest wrecks in Scapa Flow. Lying upside down, it's a massive and challenging technical dive, rewarding those with the training to explore its vast hull.