In Waitomo Nash, Grant, Luke, and I (plus another couple and our guide) went blackwater rafting. We dressed up in wetsuits, boots, and helmets, then drove about 20 minutes to a farm. We got out and walked across a cow / sheep pasture, picked up inner tubes...
walked across another hill...
then walked down into the cave entrance.
At one part of the cave we got down on our hands and knees to crawl through a small opening that had about 10 inches of (very) cold water in it. At the other end of the opening was a small room, with a waterfall pouring into it.
Here's another area where we were wading through waist-deep water.
And then we got into the inner tubes, formed a chain, and floated for a while. At the top of the cave in several areas there were thousands of glowworms. We all turned out all of our lights and walked or floated along in the dark, looking at the glow worms on the ceiling. 
And finally, coming out of the cave. It took us a while for our bodies to get warmed up again - we went back and had a hot shower and some soup.
Here's a photo of the glow worms. You cannot see them very well, but they are small worms (larvae of some insect), about 2 or 3 cm long, and they stay at the to of the ceiling of a cave in the dark, and dangle these threads down to catch passing insects. When an insect becomes caught in these threads, the glow worm pulls up the thread and eats the insect. The tail end of the glow worm lights up in green, so when its dark in the cave, you look up at the ceiling and see thousands of these tiny green lights. It is one of the most amazing things I have seen in my life.
