This story appears in the August 2018 issue of National Geographic magazine.

View Images Indonesia has 127 active volcanoes. Only the U.S. (168) and Russia (144) have more. NGM MAPS

T MINUS SIX MONTHS

A volcanic dream: I’ve been wanting to document how people live and work in extreme environments, because that may teach us how to adapt to a changing planet. Mount Ijen in East Java, Indonesia, is an active volcano that contains an acidic lake and a sulfur mine. Deep in the crater, in air heavy with toxic gases, miners extract chunks of sulfur. They carry 150- to 200-pound loads to the rim and then down the mountain to sell to factories, which use sulfur in the manufacture of things like cosmetics and sugar.

T MINUS THREE DAYS

Essential packing list: We landed in Java and drove for three days to reach Mount Ijen. While preparing for the trip, I learned that the sulfurous gas is unpredictable. Sometimes it’s so thick you can’t see or breathe. If that happens, I was advised, don’t panic—just wait for the wind to move it along.

Goggles

Water and energy bars

Heavy jacket for nighttime temperatures

Headlamp

T MINUS ONE HOUR

Ready for launch: At the foot of the volcano, I rented a gas mask. From there we climbed to the mountain edge, where tourists flock after dark to see blue flames from the combustion of gases. But if you just take a beautiful picture of the flames, you miss the human story. The miners choose nighttime to descend into the crater and do their backbreaking labor because it’s cooler. I wanted to go into the mine. At 2 a.m. I followed them into the crater to spend the night.

BY THE NUMBERS

7,100

Elevation of sulfur mine, in feet

1112°F

Temperature of sulfuric gases released from the cracks