I was deep in the tropical rainforest, several steps behind Bernardo Perez, my Costa Rican guide, when I heard a deep rumbling sound. Then, as though a prehistoric beast was thundering through the brush, the ground began to shake. I did a quick shoulder check. The volcano that loomed behind us looked peaceful but was definitely spewing more smoke than usual. But, putting my misgivings aside I followed the guide deeper into the forest.

We were hiking in the rainforest at the base of Arenal Volcano, about 75 miles northwest of Costa Rica's capital city of San Jose, and I had good reason to be worried. In a country with more than 100 volcanos, Arenal is not only considered the most active, but is also one of the world's most dangerous. A week earlier, a series of eruptions had rocked the northern face of the volcano, spewing an avalanche of stone and gas that forced the evacuation of nearby locals and visitors.

I'm not really a "lava junkie" (a volcano chaser), so why would I choose the dangerous northern side for my nature walk, instead of other safer slopes? The attraction was Arenal Hanging Bridges, a 620-acre nature preserve that features a 2-mile hike through old-growth rainforest traversing a series of bridges, tunnels and trails. The bridges include eight fixed bridges, ranging in length between 26 and 62 feet, and six suspension bridges between 157 and 322 feet long.

The trails bring visitors close to some of the densest and most diversified forest in the world. Centuries of volcanic eruptions have contributed to a mineral-rich soil that supports many species of animals and birds.

"A dart frog. Very poisonous," said Perez, pointing to a glossy red shape on a broad leaf. "And there. Do you hear that noise?"

I did, it was much like the sound of a creaking door.

"It's a chestnut-mandibled toucan. It's the largest, but not the prettiest of the species." he explained, pointing to a large bird sitting like a sentinel with an enormous yellow snout.

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 Perez, pointing down. Leaf-cutting ants, in perfect formation, each carrying brilliant emerald green bits of leaf, were winding across the trail.

With a full dance card of wildlife in Arenal Preserve, it is easy to forget that it is in the shadow of a volcano. In ancient times, the Guatuso Indians, who once lived in the area, believed the volcano was home to the God of Fire and regularly performed rituals intended to control destiny. Until July 29, 1968, people considered the volcano to be dormant. Then it suddenly erupted, sending out shock waves, hot gases and rubble. By the time it settled, it had destroyed two villages and killed 78 people. The two new craters it spawned continue to belch ash and rock to this day.

Yet, visitors continue to be drawn to its compelling beauty.

But, because the area is still considered a danger zone, several safety precautions are in place. A seismographic network issues warnings of impending eruptions and the Smithsonian Institute has a monitoring station on the south side of the volcano. Evacuation routes are clearly marked.

The volcano's dark history added some sobering thoughts to the final leg of our hike. I paused to admire a red shrimp flower being pollinated by a tiny hermit hummingbird.

"Stop, I smell monkey poop." said Perez, pointing high above us.

Sure enough, despite the unscientific announcement, there were dark shapes moving high in the canopy. Spider monkeys -- a rare sighting compared to the more common howler monkey -- danced through the trees, looking like large shadowy people... their long black arms stretching across the branches.

Then, like a giant clearing his throat, the volcano rumbled. The shrimp flower quivered.

Beauty and danger - an irresistible combination.