“It sounded like a roaring train,” said “Sweeny” Sewell, describing the noise a second before a waterfall exploded into Hang Son Doong through the Watch Out for Dinosaurs doline, or sinkhole opening. A rare dry-season downpour produced the thundering runoff. Were the cavers scared of drowning? “Maybe if it were a smaller cave,” said expedition leader Howard Limbert, “but not here.”
Nearly a thousand feet under the ground, massive beams of selenite dwarf human explorers in Mexico’s Cave of Crystals. The crystals, among the largest yet discovered on Earth, were found by two brothers working in the Naica mine, which produces lead, zinc, and silver.