Mt. Rinjani is not afriendly volcano. When it goes, it ejects ash more than 2 miles high and deposits sulfur as far away as the Arctic. Some scientists think that Mt. Rinjani alone caused the second ice age. That’s a lot of pent-up volcanic violence humming beneath my boots as I trudge up its eastern flank.

Many people visit Mt. Rinjani on the island of Lombok for this thrill. They want to get close—maybe uncomfortably close—to the seat of geothermal power. I get that, but it’s not why I’m here. For me, the risk is a means to an end, the gateway to some of the most exotic scenery on the planet and for sure its prettiest lake.

Earlier in the morning, I met up with my guide Bangko in Senaru, the waterfall-filled village north of the volcano. The 26-year-old local makes a living taking tourists up Mt. Rinjani on slower three-, four-, and even five-day jaunts, but we opt for the most direct route: a 5-mile StairMaster of a climb that gains more than 8,000 feet in a straight shot to a campsite on the caldera. I knew it’d be steep, but with several porters hauling our overnight gear, I envisioned a leisurely stroll to the summit, cheerfully spotting cockatoos and orchids.

I was wrong.

It takes nine hours. Somewhere along the way, I see a pair of trekkers turn back and I consider following them. Right about the time the eggy, sulfuric smell of the volcano wafts through the humid jungle, mingling with the sweet aroma of vanilla and edelweiss, I want to puke. I take a seat beneath a wild fig tree and watch a small black monkey swing through the climbing palms. A wild pig scampers into the underbrush, and I hear the cough-like call of a barking deer reverberate through the rainforest.

Convinced I’m rested enough, Bangko continues up the trail, his plastic flip-flops demonstrating magical stickiness on the slick dirt and roots. Near hour seven, the dark confines of the jungle give way to an open-air scene as we burst above treeline and into the clouds. The animal rustles fade as we cross volcanic scree. Through a break in the fog, I spot the island of Gili Trawangan floating in the Bali Sea.

When I finally top out, I’m ready to pummel Bangko for his insufferable fitness, cheer, and flip-flops. But when I peek out beyond the rim, the sun is dropping over the crater, 19 miles wide, flooded with sapphire sulfur water. Plumes of smoke drift from the vent of Barujari, a tiny island poking a few hundred feet up from the middle of the blue. Mt. Rinjani’s summit looms in the background, a menacing hunk of hardened magma rising from the rainforest.

Back at our tent, just below the caldera rim, Bangko gives me a hug and a high-five, then surprises me with a large bottle of Bintang beer he lugged all day for just this moment. I mutter out a humble terima kasih, Indonesian for thank you, and decide to toast him for all his help today. And his flip-flops.

DO IT From Lombok, take a three-hour bus ride to Senaru. guide Required; Adi Trekker charges $200/person for the writer’s two-day trip. Season April to July (dry season)