Black water rafting — floating through underground rivers on rubber inner tubes — is the adventurous alternative to the standard glowworm cave tour. The Black Labyrinth tour, the most popular option, involves a three-hour journey through underground rivers and waterfalls, including a jump backwards off a small underground waterfall into the darkness. The ceilings throughout are lit by glowworms.
The Black Abyss tour goes deeper and includes abseiling down a 35-metre shaft and ziplines before the river section. Both tours are run by Legendary Black Water Rafting Co. Wetsuit, helmet, and light are all provided. You'll get cold and wet, which is part of the experience — hot soup and a bagel at the end are included. Minimum age is usually 12; check conditions when booking.