The most beautiful landscapes of Kauai, along with the Waimea Canyon.
Try even a small part of the 11 miles trail, let say the firt half mile (or 2 miles = 4 miles roundtrip, to hanakapi'ai beach, as we did) and you'll be highly rewarded. Our son did the hanakapi'ai falls (8 miles roundtrip) and another day the Hanako falls (14 mile roundtrip) and much enjoyed them. Until Hanako no need of permit (this is relatively new, our Lonely Planet still inform that you need it behind hanakapi'ai but this is not true anymore). For the last segment of Kaialau you need a night-permit (even if you intend to do it in one day, which is hard but possible) - easy to get it online but allow at least 2 weeks, and in high season probably much more than that, as permits are limited.
Do not miss the nearby Kee beach.
For permit: https://camping.ehawaii.gov/camping/all,details,1692.html
It is said the car breaks are frequent here although we saw no evidence of that. Come earlier to get a parking near the trail head: more convenient and more safe at least until 4 PM when the lifeguard finish his day.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC