The Mountains above the holes at Princeville nearest the entrance road have numerous (and epically beautiful) waterfalls cascading down their faces. This is, of course, if you can see the cliff walls due to the clouds that blanket them. The waterfalls come down from the interior of Kauai, the rainiest spot on Earth.
I imagine the same phenomenon can be witnessed on the Pali Mountain cliffs above Koolau and Luana Hills on Oahu, and I'm sure there are some natural waterfalls to be seen at the Lanai twosome, among others.