Guwahati, Nov. 14 -- By Jyoti Thakur, Pratik Chakarborty

It's an autumn morning at Mawmluh Cave, near Cherrapunji, in Meghalaya's north-eastern hills. At the entrance, 27-year-old Milton Marak switches on his headlamp, and leads a group into the darkness.

There are no electric lights inside. Only the beams from visitors' torches illuminate towering stalagmites, delicate soda straws and curtains of calcite hanging from the cave ceiling.

Marak was 18 when he first crawled into the Mawmluh Cave with nothing but a borrowed torch. Trained over two years, he knows the 7.2 kilometre cave well enough to navigate its passages without a map.

"We've deliberately kept the cave natural," he says. "If we install lights, it becomes a showroom. The r...