Here's some pics of the hike my brother and I took on the last day we were in Kuaii.
This was the entrance to the first 1 mile tunnel we had to go through. Then it was a 1/4 mile walk up a river (actually in the river) to a 2nd tunnel that was 7/10 of a mile, smaller, and deeper water in it.
After almost 4 hours of hiking, this was the reward:
Actually had to piece 3 pictures together to get the whole scene, but you get the idea.
...and, found out later it's not to wise to do this:
Read later in a guide book several people have been hurt or killed from rocks coming over a waterfall.
The picture of the waterfall doesn't really do it justice, it's a lot larger than what it appears.
After the picture of me backing into it, I was walking in behind it and thought it would be cool to just walk through it. Knocked my butt striaght down to the bottom. Fortunately I didn't get hurt!