A raised boardwalk leads 3.1km (3½ to four hours return) through swampy old-growth rainforest to the mouth of the Great Cave, a vast cavern approximately 2km long, up to 250m across and up to 60m high. Inside, the trail splits to go around a massive central pillar, but both branches finish at the same point, so it’s impossible to get lost if you stick to the boardwalk. The stairs and handrails are usually covered with guano, and can be slippery.
The rock formations are spectacular and ominous by turns, and you may find yourself thinking of Jules Verne’s Journey to the Centre of the Earth. When the sun hits certain overhead vents, the cave is penetrated by dramatic rays of otherworldly light. When you’re halfway through the dark passage known as Gan Kira (Moon Cave), try turning off your torch to enjoy the experience of pure, soupy blackness.