Ecuador’s Galapagos Islands are rightly considered one of the world’s natural treasures. The unique, fearless animals that evolved on this isolated archipelago helped inspire Charles Darwin’s supreme scientific insight after his visit in 1835. It’s an incredible feeling to be surrounded by thousands of birds, reptiles and other creatures that simply don’t care that you’re there, from blue-footed boobies -- a kind of seabird -- to baby sea lions and beyond.

If you want to visit the Galapagos you must be on a guided tour, a measure that helps protect the ecosystems and wildlife; the tours suggested here are all-inclusive except for airfare from mainland Ecuador. And since you have to fly 1,000 miles from the mainland to the islands, they’re not all that cheap to visit. But it’s hard to find anyone who’s visited the Galapagos who didn’t think it was worth every penny.

5…Commune with giant tortoises

Santa Cruz Island is the geographic and economic center of the Galápagos, with nearly half of the islands’ 25,000 residents living in or near the city of Puerto Ayora. The green, misty highlands are a relief from the dry, rocky coastlines that ring most of the islands. A good road climbs four miles from Puerto Ayora to the town of Bellavista, near which are two huge lava tunnels you can climb down into. They formed when flowing lava cooled on top but kept going inside, leaving a tunnel big enough for a subway.

As the road continues to the town of Santa Rosa, it passes the Mariposa Farm, a working cattle ranch that offers snacks, lunch and what may be your first glimpse of the famous giant tortoise. These massive reptiles, found only here and in the Seychelles, can weigh more than 500 pounds and live well over a century—actually, nobody is really sure how long they can live. Their numbers were severely depleted during the 19th century, when whaling ships would stock up by the hundreds to have fresh meat at sea, but modern breeding programs have helped them recover somewhat.

Many more tortoises live in El Chato Tortoise Reserve near Santa Rosa, which covers the island’s entire southeast corner. A pair of giant volcanic craters called Los Gemelos (“The Twins”) gape near the road near Santa Rosa.

4…Gaze into an active volcano

Many tours don’t give the largest island in the Galapagos more than a quick stop, which is a shame. Formed by five volcanoes joined by repeated lava flows, Isabela is home to just a few thousand people, most in the sleepy town of Puerto Villamil on the southeastern corner. A mile-long trail from town leads to a giant tortoise breeding center run by the Galapagos National Park Service. Workers are raising about 900 turtles in safety here, including 65 adults, before reintroducing them to the wild. Five distinct subspecies of giant tortoise have evolved in the moist highlands, one on the island’s five volcanic peaks.

One of these, Sierra Negra (4,900 ft.), makes a great day hike from Puerto Villamil. It’s one of the most active volcanoes in the Galapagos, erupting most recently in 2005, so only go with a guide who is up-to-date on the current situation. The massive caldera covers almost twenty square miles, though, so a safe spot is almost guaranteed. At the edge of the caldera, you’ll be walking across rough black lava, which provides the perfect setting for a view into the volcano’s active, smoking vent.

3…Visit one of the planet’s most unspoiled places

The westernmost island in the Galápagos is one of the most pristine island ecosystems on Earth. Even though it saw lots of whaling traffic during the 19th century, Fernandina hasn’t suffered the ravages of invasive species such as goats, pigs and feral cats, like other islands have. Many tour guides will tell you that Fernandina, the youngest and most volcanically active island in the Galapagos, is their favorite.

Fittingly, there is only one visitors’ site on Fernandina. Punta Espinosa, on the island’s northeast corner, is as rough with lava as most of the rest of the island, thanks to ongoing eruptions that started in 2009. The largest colony of marine iguanas in the archipelago calls this place home. The only truly seagoing iguanas in the world, they can hold their breath for up to an hour as they munch seaweed from submerged rocks. When you see one “sneeze,” it’s not because it’s sick—it’s actually expelling excess salt from seawater through special glands in its nose.

Farther down the trail are a number of unkempt mounds made of sticks and seaweed. These are the nests of the rare flightless cormorant, which over time has lost the ability to soar—along with most of its wings and feathers—because the islands have no predators to escape from. The cormorant sure can swim, though, with a snakelike neck and large webbed feet for pursuing fish. Watch for males returning with gifts of food for females who guard the eggs, and for cormorants drying their stubby vestigial wings in the sun, almost as if they were yearning for their lost talent.

2…Paddle a sea kayak, camp on the beach

One of the most intimate and memorable ways to experience the Galapagos Islands is on a sea kayak tour by ROW adventures. Instead of sleeping aboard a boat or in a hotel, you’ll spend two nights camping on a beach on San Cristobal Island. In the highly choreographed world of Galapagos tourism, this feels a little like spending the night in a museum; you’d swear you have the place all to yourself.

The tour also takes you to other islands, including Isabela, Santa Cruz and Santa Fe, meaning you see a good cross-section of the major visitor sites. But it’s the up-close-and-personal encounters you can only get with a kayak and tent that make this one special: paddling past the towering pyramid of Kicker Rock, sliding up onto the sand at the end of the day, and waking to legions of fiddler crabs cleaning the beach.

1…Swim through an underwater wonderland

If the Galapagos qualify as amazing on the surface, they’re downright spectacular underwater. A collision of warm and cold ocean currents brings together an incredible assortment of marine life around the islands. With chilly water temperatures and occasionally strong currents, it’s not a place for novice divers, but even moderately experienced ones will think they’re swimming through an aquarium: sea turtles, dolphins, whale sharks, rays, and other large marine species appear on almost every dive.

Even if you’re not a scuba diver, there’s a lot to see with just a snorkel and a pair of fins. You might catch marine iguanas munching algae or see a tiny Galapagos penguin zoom by in a trail of bubbles. Playing underwater tag with a wild sea lion is an unforgettable experience. If you can, visit Wolf and Darwin Islands on the northern edge of the archipelago, where the odds are best of spotting whale sharks and schools of hammerheads.