As summer hits its stride and the sun-soaked days grow longer, days by the pool sound more and more enticing. While it's unlikely that your visions of a relaxing vacation include a jaunt up a volcano, perhaps they should. These geological landforms are incredibly powerful and deserve a healthy dose of respect but if approached correctly, can be an astonishingly rewarding and unique adventures. Strap on those hiking boots and start exploring these lava-spitting, gas-spewing, ash-throwing marvels.

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Thrihnukagigur - Iceland

Thrihnukagigur is the only volcano in the world whose innards are open for public exploration. Yes, we said inside. As you approach the 100 foot-tall cinder cone on foot, you’ll stop by the base camp owned by Inside the Volcano. Certified by Iceland’s administration of Occupational Safety and Health, Inside the Volcano leads small groups through one of three magma chambers in this dormant volcano on a daily basis.

Access is only possible through a tiny 12-foot opening. As you slowly sink into the heart of the volcano through the open elevator, hard hat and harness firmly in place, you’ll be enveloped in an eerie silence. The outside of Thrihnukagigur is not a particularly impressive site, but the inside is a different matter. As you disembark from the elevator, be sure to note the natural colors coating the jagged walls. Past gases, pressures and extreme temperatures have stained the interior an intriguing palate of yellows, reds and blacks. Explore to your heart's content and then head back to base camp and finish off your trip with a warm mug of coffee and a bowl of Icelandic stew.

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Whakaari Island - New Zealand

Stepping onto Whakaari Island is akin to landing on another planet. Craters belch plumes of white steam. Gases roar and hiss. The smell of sulphur is overwhelming and brown cliffs are stained red and yellow from volcanic activity. This marine volcano lies 48 km off the coast of New Zealand and consistent activity keeps the landscape in a constant state of flux. Similar to an iceberg, most of the volcano’s mass is underwater, yet the crater is visible above the surface. A convenient gap in its side allows visitors to step directly off their boat and onto the volcano.

The island is privately owned and only a few select tour companies like Pee Jay’s White Island Tours are allowed to show visitors its wonders. Summiting the volcano is forbidden, but visitors will be led on a route around the crater, past hot springs, bubbling mud, and a steaming lake of acid, accompanied by helpful commentary about the geology and history of the island.

Mt. Stromboli - Italy

This “Lighthouse of the Mediterranean” is one of the most active volcanoes on earth and will light up the night sky like nothing you’ve ever seen before. Erupting consistently at 20-minute intervals, it has regularly hurled fiery sparks and incandescent blots of lava above the crater rim for at least 2,000 years.

Those that come to witness Stromboli’s eruptions, arrive by boat only: cars aren’t allowed on the island. Their journey from sea to summit takes only three hours by foot and concludes with a spectacular display of volcanic activity. Be sure to go in the evening hours for the best views of the lava illuminating the darkness as it flows down the inky black slopes.

Maelifell - Iceland

Many volcanoes are considered significant because of their lava flows, their height, the rate of volcanic activity . . . but we like Maelifell Volcano in Myrdalsjokull Glacier Park because its just plain pretty to look at. Its startlingly green grassy sides dramatically contrast the surrounding black and white landscape that is best explored by Super Jeep. Tour companies like Extreme Iceland offer long day trips out of Reykjavik to the volcano, but you can also rent a 4x4 to explore the area on your own if your prefer to control the schedule. Either way Maelifell is sure to be an unforgettable part of your trip to Iceland.

Mount Nyiragongo - Democratic Republic of the Congo

Virunga National Park is one of the most biologically diverse areas on the planet and Africa’s oldest protected national park. Lions stalk the savannas, hippos romp in the rivers, gorillas dangle from trees, and the world’s largest lava lake sits nestled in the bowels of Mount Nyiragongo.

The mountain is one of eight edifices in Virunga’s volcanic field. Its cone shape and 50 degree slopes near the summit makes it a challenge to climb, but trained park rangers are more than capable of guiding you to the top safely. The main summit crater is a steep-sided pit, about 1.2 km wide. Multiple terraces step down to the bubbling mass, marking the locations of former lava lakes. As mesmerizing as the cracked glowing surface looks, forego the swimming suit and just enjoy the view.

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Mt. Karthala - Comoros

Set in the dense jungle on the southern tip of Grande Comore, Mt. Karthala is the largest active volcano in the world and is responsible for creating the very island on which it stands. Creating most of the island’s bedrock, there are no permanent rivers or lakes as standing water quickly seeps through the porous surface and disappears.

The massive shield volcano occupies more than 60 percent of the island’s surface so give yourself a full day to hike to the top. The path leads through the jungle, across shrubby grassland, and finally onto fields of black ash surrounding the edge of the enormous caldera. The journey from the native village to the tip of Mt. Karthala is not for the faint of heart or weak of legs, but every step through the dense vegetation and up the monochromatic slopes of ash will be worth it.