The Redwoods Glowworm eco-cave in Whakarewarewa Forest opened in 2018 as New Zealand's first purpose-built bioluminescent grotto, replacing the need for visitors to scramble through fragile limestone formations. Engineer Peter Elley designed the 120-metre subterranean corridor to mimic the humidity, darkness, and airflow that Arachnocampa luminosa larvae require, installing misting systems that hold moisture at 85 percent year-round. The structure sits ten metres below the forest floor, insulated by compacted clay and a living roof of ferns that stabilise temperature swings to within two degrees Celsius — conditions wild caves struggle to maintain as visitor numbers rise. Glow worms are not worms but the larval stage of a fungus gnat, and their cold blue-green light is a predatory lure. Each larva suspends up to seventy silk threads coated in mucus droplets, then illuminates its tail using luciferin and the enzyme luciferase to attract midges and mayflies. The threads act as snares; once an insect tangles, the larva reels it upward and consumes it. A single larva glows for six to nine months before pupating into a short-lived adult gnat that neither feeds nor glows. The Redwoods eco-cave hosts several thousand larvae at any given time, their constellations densest along the timber boardwalk's final thirty metres where moisture condenses most reliably. Rotorua's geothermal zone provides an unusual advantage: the soil temperature beneath the forest remains stable, and the eco-cave taps groundwater warmed by subsurface heat to regulate the misting system without mechanical refrigeration. The site lies within the Whakarewarewa Forest, a 5,600-hectare plantation of Californian redwoods established in 1901 to test exotic timber species on volcanic soil. Those redwoods now tower forty metres above the eco-cave entrance, their canopy dense enough to filter daylight into the diffuse green half-shadow that glow worm adults favour for mating. A rotorua glow worm cave tour runs every thirty minutes between 09:00 and 17:00, with each group limited to fifteen visitors to prevent CO₂ buildup that can extinguish the larvae's glow. The boardwalk descends at a gentle 1:12 gradient, accessible to wheelchairs and prams, and the cave maintains 14 degrees Celsius regardless of the season outside. Guides enforce a no-flash-photography rule; camera sensors capture the bioluminescence only with exposures of eight seconds or longer, requiring tripods that block the narrow walkway. The eco-cave model has since been replicated in Waikato and Canterbury, but Rotorua's remains the largest by larval density and the only one embedded within a redwood forest microclimate.