Waitomo's cave ceilings glitter with thousands of tiny blue-green lights, but they are not stars — each is the glowing tail of a fly larva. The animal behind the spectacle, Arachnocampa luminosa, is a fungus gnat found nowhere on Earth but New Zealand; in the dark its larvae dangle sticky silk threads and burn a cold, living light to lure insects to their death. The caves that shelter them were dissolved from soft limestone by the Waitomo Stream over millions of years — 'wai' means water and 'tomo' means hole. Local Maori chief Tane Tinorau knew the entrance as a fishing spot, and in December 1887 he and English surveyor Fred Mace floated in on a flax raft by candlelight, beneath the living ceiling of the Glowworm Grotto. The cave opened to visitors two years later; in 1989 the land was returned to Tinorau's descendants, who own it still.
The heart of a visit is a boat ride no one speaks through. A guide pulls the craft along an overhead rope, the last lights go out, and the grotto's roof resolves into a galaxy of cold pinpricks mirrored in the black water below, so still you can hear stone dripping. Cameras and flashes stay off — partly to protect the larvae, which dim when startled, and partly to keep the dark complete. Deeper in, the caves open into the Cathedral, a chamber over thirteen metres high whose acoustics have drawn choirs and carol singers, and into passages hung with stalactites. Around half a million people come each year; those who want the caves on rougher terms head to neighbouring Ruakuri, where black-water rafting floats you down the underground river in a wetsuit and rubber tube, the glowworms strung overhead.