Black Water Rafting and Fluorescent Worm Larvae

One of the most varied and fascinating places to head underground must surely be Waitomo Caves. This natural cave system, 200km (125miles) South of Auckland on the North island, consists of 3 different subterranean experiences; The Glow-worm Caves, Ruakuri Caves and Aranui Caves.

The glow worm caves, are a series of underground caverns which carry an underground stream with thousands of luminous, glowing worms hanging from the roof. You can take a ride down the stream with a guide to learn a bit more about the unusual worm, Arachnocampa luminosa, known to the Maoris as Titwai. It's the larval stage of the insect which glows in order to attract prey into sticky threads of silk it dangles below itself to trap prey before hauling it up.

With its stunningly-architected spiral stair down to the cave entrance, you know you are in for something  special as you descend into Ruakari. The caves were first discovered almost half a millennium ago by a wandering Maori hunter when he was attacked by dogs who were using the mouth of the caves for refuge. Although you can travel the winding 1.6 km (1 mile) system on foot across heady walkways, Ruakari is where the infamous black water rafting takes place. Not as scary as it sounds, the caves have an excellent safety record for their trips where you ride what looks like a truck inner tube down the cave river in a wetsuit and helmet. Some of the access is not for the faint-hearted though as it involves a high abseil and a squeeze through some rocks to the rafting point.

For the perhaps less adventurous and more geologically-minded, the smaller and drier Aranui caves offer a spectacle of rock formations including stalactites, wetas and flowstones formed in delicate brown, pink and white limestone. Named after the local Maori man who discovered the cave system, Aranui is a place sacred to the Maori and with an air of magic about it. Aranui is situated close to the Glow worm caves if you want to experience both and is suitable for all ages as long as you're not bothered by the large crickets which live in crevices near the entrance...

Exeter Underground Passages

Find yourself in Devon with some time on your hands and some spare old clothes? Located under the city centre, just off the High Street is a labyrinth of medieval passages dating back to the 14th century. The tunnel network lies inside the city wall perimeter and was originally built to house pipes to bring fresh drinking water to the clergy of the city, and later, to the wealthy merchants who could afford to have water piped to their homes. In around1643, at the beginning of the Civil War, the entrances to the tunnel network were blocked off and the tunnels filled with rubble to prevent invasion. The lead pipes were stripped and used for making munitions. The tunnels and supply of water were restored shortly after the war.

Following a Cholera outbreak in 1832, the connection was made between a water's cleanliness and the likelihood of infection and the engineer Thomas Golsworthy was commissioned to improve the system. He replaced the lead pipes with steel, lowered the floor and made it more even which, resulted in less leaks and improved flow.

The majority of the nearly 500 metre tunnel system are vaulted to prevent cave-ins and allow easy maintenance access to the old pipe system. After abandonment as a water supply in 1857, the tunnels were more or less forgotten until providing a crucial function as bomb shelters during Word War 2 air raids. Exeter blitz devastated much of central Exeter's shopping arcades, civic centre and a section of the 12th century gothic cathedral.

The tunnels are today open to visit on a guided tour starting at the visitor centre in Paris Street.