Our very excellent guides.
We traveled along two and a half miles of an old sugar plantation irrigation system. The particular route we were on is still in use as a water delivery system into a purification plant and then distribution to Kapaa, Lahui, and a few other towns in Kauai.
We spent a lot of time in the tunnels that plantation workers dug by hand in the early 1800s, which reminds me to note that the guides did an excellent job of keeping us all entertained with interesting stories and audience participation for the three hours which included only about 45-60 minutes of actual tubing.