Waitomo is a limestone cave in the Waikato region of New Zealand's North Island whose ceiling glitters with thousands of glowworms, the larvae of a fly found nowhere else on Earth, and the way to see them is from a boat on an underground river, pulled by hand in silence. The glow is a trap. Each larva hangs a dozen threads of sticky silk from the ceiling and lights its tail blue-green to lure insects into them, and the hungrier it is, the brighter it shines; a cave full of them looks like a night sky, and the guide drifts the boat beneath it with the lights off and no one speaking, because noise makes them dim. The limestone around you began as sea floor, shells and coral laid down 30 million years ago, lifted and cut by water into the caves, and the tour walks first through the upper levels, past stalactites and the Cathedral, a high-ceilinged chamber with acoustics good enough that singers perform in it, before descending to the river and the boat.
The caves were opened in 1887 by a local Māori chief, Tane Tinorau, and an English surveyor, who explored them by candlelight on a raft of flax stems; his descendants own and run them still. The neighbouring cave, Ruakuri, holds the wilder version: black-water rafting, three hours of floating and leaping down underground cascades in a wetsuit and inner tube, glowworms overhead and a hot shower at the end, and abseiling into the caves for those who want the rope. Ruakuri also has a walking tour through a spiral entrance built so that the cave's sacred burial site is not disturbed. The village of Waitomo is a few houses and a road in green farmland, and the caves under it are the reason it is on the map. Waitomo is a river you take a boat down under a sky of insects, and the sky is hunting.