New Zealand
In the North Island, it would be Waitomo Caves. In the South Island, there is a cave complex in Nelson region, and it contains Harwood's Hole, an exceptionally deep cave system, still being explored. Further south, at Te Anau, there are the Te Anau glow worm caves. Harwood's Hole is not a commercial venture, because of dangers and the level of experience needed. The Waitomo and Te Anau caves both have organized tours.
Waitomo Caves Hotel was created in 1908.
Waitomo Glowworm Caves was created in 1889.
Blackwater Rafting also called Cave Tubing is like whitewater rafting but in caves. It is especially popular in Waitomo, New Zealand.
I think you are enquiring about the underground cave systems. Either those of Waitomo in the North Island, or those of Te Anau Au of Lake Te Anau in the South Island. Both have well developed tourist industries.
Hotels in Waitomo can be researched and reviewed on Travelocity, Expedia, Hotels, TripAdvisor, and the Waitomo Island official website. These beach side hotels are all very nice.
Deep, deep down
The cave system of Lascaux is approximately 200 meters long and consists of several chambers and corridors. The main part of the cave, where the famous prehistoric paintings are located, is about 20 meters below the surface.
2 stories deep
Gardiners Gut is the longest cave in the North island of New Zealand and Hagga honking holes is the name of an exciting adventure at the Waitomo caves in New Zealand
848 miles