1. Bioluminescent Bay

Located in Puerto Rico, on Vieques Island, there is a shallow body of water with a narrow inlet known as Mosquito Bay. In each gallon of the bay there are 720,000 phosphorescent single-celled organisms that glow when they are agitated. It is a defense mechanism — the glowing is designed to daze whatever predator is bothering the tiny dinoflagellates. All together the bay, on a moonless night, will produce more than enough light to read. Swimming in Mosquito Bay will cause your limbs to be bathed in blue-green light. If you stop moving the light will dim, and eventually disappear completely, but each time you twitch it begins anew. Every time your kayak moves it too will be illuminated. It’s also easy to spot larger creatures; when manta rays or large jellies enter the mangrove swamps gentle rings of light form around them. If you scoop up a handful of the water you can watch individual glowing plankton roll down your arms and hands. And the salinity of the water, like the Dead Sea below, is high enough you can float sitting upright. Photographing Biobay isn’t easy, so there aren’t many high quality pictures of it, but enjoy the ones we found below.

2. Jellyfish Lake

12,000 to 15,000 years ago one of the limestone rock islands in the nation of Palau sealed itself off from the ocean and became a marine lake. A few jellyfish were sealed inside, and with virtually no predators, they began multiplying and evolving. Today more than 10 million jellyfish inhabit Ongeim’l Tketau, known as Jellyfish Lake to tourists. Their sting became evolutionarily useless, and has been lost over time, to the point that the jellies are completely harmless to swim with. Swimming in Jellyfish lake, surrounded by a translucent sea of rhythmically pulsing creatures, is known to be unbelievably serene. The jellies, varying in size from basketballs to blackberries, slowly undulate as they follow the path of the sun across the surface of the lake.

3. Devil’s Swimming Pool

The Devil’s Swimming Pool, or Devil’s Armchair, is a naturally formed infinity pool at the very top of Victoria Falls in Zambia. 420 feet above the river below, it is perfectly safe (in the dry season) to relax at the edge of one of the world’s largest waterfalls. From above the water it appears as if there’s nothing to stop one from being carried over the lip of the falls, but beneath the surface there is a natural rocky ledge that generates a back-eddy and stops the current. Looks scary, especially to jumping into, but the thousands of still-alive visitors can attest to its perfect safety record.

4. Dean’s Blue Hole

In a bay west of Clarence Town on Long Island, Bahamas, is the deepest underwater sinkhole in the world. It plunges 663 feet to the ocean floor, making it vastly deeper than other blue holes (The Great Blue Hole in Ambergris Caye, Belize is 410 feet deep, and the Blue Hole in Sinai, Egypt is about 420 feet deep). Dean’s is known worldwide as the perfect spot for free-diving; it was the location over the last few years of numerous new world and national free-diving records. The blue hole is roughly circular at the surface, with a diameter ranging from 25 to 35 metres (82–110 ft). After descending 20 metres (66 ft), the hole widens considerably into a cavern with a diameter of 100 metres (330 ft). If you prefer marine life to extreme breath-holding, however, I might recommend The Great Blue Hole in Belize. I snorkeled and dove it in 2007, and was enthralled with the crystal clear water and huge number of large fish and sharks. It was the first place I encountered a wild Blacktip reef shark, a wonderfully beautiful place. Jacques-Yves Cousteau declared it one of the top 10 scuba diving sites in the world. See a gallery of pictures of the Great Blue Hole below.

5. Zacatón Cenote

Zacatón is one of a group of five interconnected sinkholes, or cenotes, located in the northeastern state of Tamaulipas, Mexico. It is the deepest water-filled sinkhole in the world with a total depth of 335 meters. DEPTHX, a NASA funded project using an autonomous robot has measured the underwater portion to be 319 meters deep (an air-filled 16 meter drop from the surface to the water accounts for the total depth). In a 1993 dive Dr. Ann Kristovich set the women’s world depth record of 554 feet, and on April 6, 1994, explorer diver Jim Bowden and cave diving pioneer Sheck Exley plunged into El Zacatón with the intent of reaching bottom. Bowden dove to a men’s world record depth of 925 feet, but Exley (who invented/standardized use of the “Octo” or octopus safety regulator) died, probably from high pressure nervous syndrome (HPNS) at around 879~906 feet. The name Zacatón comes from the free-floating islands of zacate grass which move about on the surface with the wind. They are visible in the pictures as the surprisingly-large circularly symmetric islands. Because they aren’t connected to the lake bed they float with the wind. Besides swimming and diving in the cenote you can swim to the islands and suntan and picnic as they slowly drift on the surface of the sinkhole.

6. The Dead Sea

The shores of the Dead Sea are the lowest land point on the surface of the Earth. Resting 1385 feet below sea level, the Dead Sea is also a hypersaline lake, one of the world’s saltiest bodies of water. It resides in the Middle East, between Israel and Jordan, and even appears in the Bible. What interests STS, however, is the level of salinity. Besides tasting awful, it also provides exceptional levels of buoyancy. The tourist in the photo is sitting in a reclined position, and the water is dense enough to support his weight. If you tried that in your local swimming pool you’d immediately sink. Apparently it’s an unbelievable sensation.

7. Chuuk or Truk lagoon

Truk Lagoon, also known as Chuuk, is a sheltered body of water almost fifty miles long by thirty miles wide surrounded by a protective reef. It is composed of 11 major islands, along with 46 smaller ones inside the lagoon plus 41 on the fringing coral reef — today part of the Federated States of Micronesia. Its interest to STS stems from its use in World War II as the forward anchorage for the Japanese Imperial Fleet. It was considered the most formidable of all Japanese strongholds. When the US Naval forces captured the Marshall Islands they launched an early morning attack on February 17, 1944 against Truk Lagoon. This was Operation Hailstone, a bombardment lasting three days that sent virtually everything of value – 60 ships and 275 aircraft – to the bottom of the ocean. Today it has turned into a divers paradise after being explored by Jacques Cousteau. It is full of ghostly remains; the waters are almost devoid of normal ocean currents so they are almost perfectly preserved. The waters are crystal clear, and some ships lie less than 15 meters below the surface. Divers can easily swim across decks littered with gas masks and depth charges and below deck can be found numerous human remains. In the massive ships’ holds are row upon row of fighter aircraft, tanks, bulldozers, railroad cars, motorcycles, torpedoes, mines, bombs, boxes of munitions, radios, plus thousands of other weapons, spare parts, and other artifacts. Of special interest is the wreck of the submarine I-169 Shinohara which was lost when diving to avoid the bombing. The sub had been part of the attack on Pearl Harbor. The coral encrusted wrecks attract a diverse array of marine life, including manta-rays, turtles, sharks and corals.

8. Yangbajain hot springs

The Yangbajing hot springs, in the Tibet Autonomous Region of China, (known to people who appreciate freedom as Tibet) provides much of the electricity for Lhasa, the capital. A thermoelectric power plant on the edge of the Yangbajain hot spring fields, which cover 20-30 square kilometers. These particular springs are so interesting because they are at an elevation of approximately 14,000 feet (about the same as the peak of Mt. Rainier in Washington State). The water emerges from the crust of the earth at 84 degrees F, which is higher than the boiling point at that altitude. The springs themselves aren’t as beautiful as some of the other locations on this list, but they have a misty charm of their own.

9. The Seagaia Ocean Dome

The Seagaia Ocean Dome was the world’s largest indoor waterpark, located in Miyazaki, Miyazaki, Japan. The Ocean Dome measures 300 metres in length and 100 metres in width, and is included in the Guinness World Records. It opened in 1993, and visitor numbers peaked in 1995 at 1.25 million a year. The Ocean Dome was officially closed on October 1, 2007. The Ocean Dome sported a fake flame-spitting volcano, artificial sand and the world’s largest retractable roof, which provided a permanently blue sky even on a rainy day. The air temperature was always held at around 30 degrees celsius and the water at around 28. The sand was made from crushed marble, which doesn’t stick to skin as much as regular does — meaning when you lay down you don’t get sandy. Check out the pictures below — what an engineering project!

10. Sistema Sac Actun

The Yucatan Peninsula is home to the longest underwater cave system in the world. Sistema Sac Actun was found to be connected to Sistema Nohoch Nah Chich, creating a system 154,783 meters long, the longest underwater cave in the world. By comparison the previous record holder Ox Bel Ha measured a puny 146,761 m. I mean that’s only 91 miles long, sheesh. The two have been exchanging the record for years as new, previously unexplored, sections are discovered. The whole system has been named Sistema Sac Actun, and is home to some of the most decorated and beautiful cave diving sites in the world. The most well known entrance is Grande Cenote, pictures of it are above and below. There is surprisingly little information about this incredible cave system, but we’ve shared what we could find. Once you get in to the system the water temperature is relatively constant, and some parts are very fragile and require perfect buoyancy. As you get deeper in the system there are incredible stalactites and stalagmites, and other geologic features.