I was deep in the tropical rainforest, several steps behind Bernardo Perez, my Costa Rican guide, when I heard a rumble like a primordial growl behind me. Then, as though a prehistoric beast was thundering through the brush, the ground began to shake. I did a quick shoulder check. The coast was clear, but the volcano looming over us seemed more menacing than it had earlier.

“What do we do if it erupts?” I asked, hurrying to catch up.

“We run,” he replied, lifting his binoculars to focus on a movement high in the canopy of trees.

“How fast does it travel?” I continued, wanting to be prepared.

“Oh, about 75 miles [120 km] an hour,” he said, pointing to a quivering broad leaf ahead of us.

I took one last look behind me, put my misgivings aside and followed him deeper into the forest.

We were hiking Arenal Volcano, 5,436 feet (1,657 m) high and located about 80 miles (128 km) northwest of Costa Rica’s capital city of San José, and I had good reason to be worried. In a country bursting with more than 100 volcanos, Arenal is not only considered the most active, but it is also one of the world’s most dangerous.

Less than a week before my visit, a series of eruptions had rocked the northern face of the volcano, spewing and spitting an avalanche of stone and gas that forced the evacuation of locals and tourists.

One of six suspension bridges in the Lake Arenal nature preserve.

I am not a “lava junkie” (a volcano chaser addicted to the thrill of danger zones), so why did I choose the more dangerous northern side for my hike, instead of other safer slopes? The attraction was a new 600-acre (2.4 km²) nature preserve near Lake Arenal. Opened in 2002, it features a two-mile (3.2 km) hike through old-growth rainforest, traversing a series of bridges, tunnels and trails. The bridges include eight that are fixed, ranging in length between 26 and 72 feet (8 and 22 m), and six suspension, between 160 and 320 feet (48 and 97 m) long.

The trails bring visitors close to some of the densest and most diversified forests in the world. Over the millennia, volcanic eruptions have contributed to the area’s dramatic beauty as well as mineral-rich soil that supports forests and homes for myriad species of animals and birds.

“A dart frog. Very poisonous,” said Bernardo, pointing to a glossy red shape on a broad leaf. “And there, over to the left. Do you hear that noise?” I did. It was much like the sound of a creaking door.

“It’s a chestnut-mandibled toucan. The largest, but not the prettiest of the species,” he explained. I looked up and there was a large bird, sitting like a sentinel with an enormous yellow beak.

I ducked as something flew straight for my hair. A crystal butterfly, its transparent wings outlined in blue like a cartoon character.

“Watch out,” said Bernardo, pointing down. Leaf-cutting ants, in perfect formation, each carrying brilliant green, round chomped bits of leaf, were winding across the trail. We stepped around as they made their way deeper into the underbrush.