In part based on recommendations found here

Two of the highlights of our visit last year were the Jack Harter Helicopter tour-door off!-90 minute tour (linked) and a Na Pali Coast boat tour with Captain Andy's: https://www.napali.com/ We did the sunset sail and even though it was April, we still did see a whale breach at the end of the whale-watching season.

The helo tour followed record-setting rains on the northern part of Kauai: "49.7 inches fell at Waipa Garden in the 24-hour period ending 12:45 p.m. on April 15, breaking the previous U.S. record of 43 inches on July 25-26, 1979, near Alvin, Texas, from Tropical Storm Claudette," so we saw hundreds upon hundreds of waterfalls that wouldn't ordinarily exist. The pilot was great and the view was breathtaking. Well worth the money.
Edit: The Na Pali Coast is a must by air or sea, and the experience is different from each perspective.

Click here for link at https://www.helicopters-kauai.com/