The Northern Arch is a spectacular, deep archway at the northern end of the Poor Knights Islands. The walls of the arch are covered in beautiful gorgonian sea fans, and its exposed position offers a good chance of seeing larger pelagic fish.

The Northern Pinnacles are the go-to spot during the summer months at Protea Banks. This deep reef is the best place to see large numbers of bull (Zambezi) sharks, as well as scalloped and great hammerheads.

Nosy Be, an island off the northwest coast of Madagascar, is a fantastic diving destination with vibrant reefs and a high chance of spotting whale sharks during their migration season. The diving is relaxed, with plenty of macro life to discover.

Nudi Falls is a unique muck diving site in Lembeh. Instead of a sandy slope, it's a small wall covered in colorful soft corals. As the name suggests, it's a fantastic place to find a huge variety of nudibranchs, as well as frogfish and other critters.

As the name suggests, Nudi Retreat is a muck diving site that is a particular hotspot for finding an incredible variety and number of nudibranchs. It's a must-do dive for anyone who loves these colorful sea slugs.

Nudi Rock is a small island in the Fiabacet chain that vaguely resembles a nudibranch from a certain angle. Underwater, it's a soft coral paradise and, true to its name, a fantastic place to find a wide variety of colorful nudibranchs.

Nungwi, at the northern tip of Zanzibar, offers some of the best and most varied diving on the island. The reefs are very healthy, and it's a great place to see turtles, Napoleon wrasse, and a good variety of macro life.

The reefs around Nusa Laut are a stunning example of successful community-based marine protection. For decades, the local village has protected the reef, resulting in some of the most pristine and dense hard coral gardens in all of Indonesia.

Observation Point is another world-class muck diving site in Milne Bay. The sandy slope is famous for being one of the most reliable places in PNG to find the rare and beautiful Rhinopias scorpionfish.

The Ocean Revival Park is a unique underwater park where four decommissioned Portuguese Navy vessels were intentionally sunk to create a massive artificial reef. It's a fantastic destination for wreck lovers, with a variety of ships to explore.

This large sea cave is where, according to legend, Odysseus was shipwrecked and held captive by the nymph Calypso. The dive involves swimming through a long tunnel into the cave, which has a collapsed roof, creating beautiful light.

The Odyssey is a massive 300-foot freighter and one of the largest wrecks in the Caribbean. It was intentionally sunk and sits upright, offering multiple levels and penetration opportunities for advanced wreck divers.

The oil platforms off the coast of Southern California have become incredible, unique artificial reefs. Their massive support structures are completely covered in colorful anemones, mussels, and scallops, attracting sea lions and vast schools of fish. A truly surreal dive.

The oil platforms off the coast of Southern California have become incredible, unique artificial reefs. Their massive support structures are completely covered in colorful anemones, mussels, and scallops, attracting sea lions and vast schools of fish. A truly surreal dive.

The oil platforms off the coast of Southern California have become incredible, unique artificial reefs. Their massive support structures are completely covered in colorful anemones, mussels, and scallops, attracting sea lions and vast schools of fish. A truly surreal dive.

Oil Slick Leap is a fun shore dive named for a giant stride entry from a cliff into the clear water below (an easy ladder is also available for exiting). The dive itself is on a beautiful, healthy reef wall.

The Okikawa Maru is the largest of the Coron wrecks. This oil tanker is covered in beautiful coral growth and is accessible to a wider range of divers due to its shallower depth. The deck is a stunning coral garden teeming with life.

The Olympia Maru is another large Japanese freighter in Coron Bay. It sits upright and is a great wreck for divers of all levels, with the deck being relatively shallow. The wreck is home to large groupers and schools of batfish.

Opunohu Canyons is a dive site with a beautiful underwater topography of sandy canyons that cut through the reef. It's one of the best places in Moorea to see large green sea turtles, and lemon sharks are often seen patrolling the area.

Orange Canyon is a beautiful dive site on Grand Cayman's west wall, named for the massive, vibrant orange elephant ear sponges that line the canyons and swim-throughs. It's a spectacular and colorful dive.

In the winter, massive schools of herring migrate into the fjords of northern Norway, attracting hundreds of orcas and humpback whales. This offers a world-class, snorkel-only opportunity to be in the water with these magnificent animals as they feed.

Orda Cave in Russia is the longest underwater gypsum cave in the world. The water is incredibly clear, offering visibility of over 40 meters. The massive, white gypsum passages create a stunningly beautiful and otherworldly environment for trained cave divers.

Oslob is a famous but controversial tourist destination where local fishermen feed whale sharks, guaranteeing sightings for snorkelers and divers. The practice is debated for its ecological impact but provides very close encounters.