I used to belong to an outing club with which I walked thru caves in southern Indiana. 'Twas interesting for a change, esp. seeing stalagmites & stalactites, but not my cup of tea on a frequent basis.

What effect do the glowworms have which people find so special?
Is there also a glowworm cave on South Island?
How tight/low does the "ceiling" get on the various black-water rafting/ tubing tours?