How to trek to two of the world’s largest known caves

It’s a four-day hike through leech-filled jungle to reach Vietnam’s Hang En and Hang Son Doong caves.

Italian physicist and photographer Alessandro Cerè took a break from work at the Centre for Quantum Technologies in Singapore to venture into Hang En and Hang Son Doong, two of the top three largest known caves in the world. To get there, a punishing path and 90 percent humidity test even the fittest hiker.

A walk for the fortunate few: Only a limited number of travelers are allowed to visit these caves each year, but Cerè snagged a last-minute spot through a friend of a friend. Looking at photos online, he knew he’d need a lens that could handle the light contrasts inside the caves and decided to invest in new camera equipment. As the trip approached, Cerè ran every day to prepare for the physical toll of hiking and climbing in the sweltering jungle.

Essential packing list: The trip poses at least one confounding packing problem: It’s wet and muddy, but nonbreathable waterproof boots can breed foot infections.

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