6 of the World's Most Awe-Inspiring Geological Wonders

Bolivia’s Salar de Uyuni is both the world’s largest salt flat and the flattest place on the planet. Toss in a tiny bit of rain and it’s also the world’s largest mirror. The Salar de Uyuni marks the spot where a massive prehistoric lake ran dry, a legacy left in neon white salt and life-defying, cacti-studded islands.

Most salt flat tours start from the eponymous town of Uyuni—get there via plane or bus from La Paz. To increase your odds of experiencing the wild mirror effect, visit during the rainy season, which typically runs from December to April.

Thousands of limestone islands—each topped with ancient rain forests—rise out of Vietnam’s majestic Halong Bay. This drowned karst landscape, as it's known to geologists, is the world’s best example of marine-invaded tower karst. That means a lot of limestone eroded over time, water rushed in and out, and a series of caves, Fengcong (clusters of conical peaks), and Fenglin (isolated towers) resulted. There’s nowhere quite like it.

Most travelers to Halong Bay take tours from Hanoi, about 3 hours away. You can also travel independently to Halong City or Hai Phong and reach the UNESCO-protected bay from there.

Just 60 miles (100 kilometers) off the coast of Belize, the Great Blue Hole has transfixed divers, sailors, and water lovers for centuries. Measuring 1,043 feet (318 meters) wide and 407 feet (124 meters) deep, the Great Blue Hole is the Earth’s largest sinkhole.

Made famous by Jacques Cousteau, the popular dive spot is part of the coral-rich Belize Barrier Reef Reserve System, a UNESCO World Heritage Site. Get there on a tour from San Pedro or Belize City, or take a helicopter tour of the Great Blue Hole to get an awesome aerial vantage point.

Insider tip: You'll need Advanced PADI Certification to dive here, but snorkeling is open to all.

Resembling 40,000 patio tiles, the perfectly hexagonal basalt columns of Northern Ireland’s Giant’s Causeway look entirely manmade. Local legend says these were stepping stones laid down by Fion Mac Cumhaill, a giant crossing the sea to fight a Scottish rival.

In fact, the columns are hardened lava that bubbled up from the Earth and cooled at a very specific temperature to create an interlacing geometric symphony. Though similar formations exist throughout the world, none can match the grandeur of Giant’s Causeway. That means you often have to share this spectacular space—come early or near dusk to avoid the worst crowds.

Insider tip: Beautiful coastal walks line this area. To avoid the parking fee, walk from either Dunserverick Castle or Portballintrae. Of course, you can always book a a guided tour of this UNESCO World Heritage Site, too.

With flora and fauna that can be found nowhere else, the island of Madagascar is one of the most biodiverse spots on the planet. One spot that embodies this mix is Tsingy de Bemaraha National Park. In Malagasy, Tsingy means “where one cannot walk barefoot”—and that’s no joke. Here, thousands of limestone spikes stand sentinel, making the ground unnavigable—even for lemurs.

To explore the park, humans can walk over aerial suspension bridges above the limestone to reach savannas and mangrove swamps. Book a tour out of the coastal town of Morondava and stay in one of the lodges in Bekopaka.

One of the best things to do on the Big Island of Hawaii is witness Hawaii's Mauna Kea. Rising 13,796 feet (4,205 meters) above sea level and extending about 19,700 feet (6,000 meters) below sea level, Hawaii’s impressive mountain clocks in at 33,500 total feet (10,211 meters)—the tallest mountain on the planet.

Dormant Mauna Kea is not far from Kilauea, an active volcano that is the highlight of Hawaii Volcanoes National Park. Witness the glow from Kilauea Crater, trek down the steaming hiking trails, or take a scenic ride down Chain of Craters Road. Meanwhile, located at 9,200 feet (2,800 meters), Mauna Kea’s visitor center makes for some absolutely spectacular stargazing.