This may be Kauai’s top hike:

Kauai has many hikes that score a perfect 10—and you just can’t get better than sublime. But the Awa’awapuhi Trail may get the top vote among many visitors. It’s freaking breathtaking. 
Just the facts: The trailhead is at an elevation of nearly 5,000 feet at the upper rim of Waimea Canyon. Distance is 6.5 miles, round-trip, with an elevation loss of 1,700 feet, though ups-and-downs make the climbing closer to 2,000 feet. The first leg of the journey penetrates a bird-rich, dry forest wilderness called the Napali-Kona Forest Reserve. More tweeting is done here than in Silicone Valley.
The termius looks straight down 3,000 feet from a Napali ridge to a little valley that is part of Napali Coast State Park. Reachable only by sea, this zone was inhabited well into the 1900s by native people.
Careful hikers and goats can venture onto a viewing knob that heightens the experience (pun intended)—though drop-off hazards are present, and this side trip is not recommended for acrophobics. 
Prepare for a for-real day hike (rain gear, food). Hiking poles will help on steep, slippery sections. Hearty families can make it. Though on the tourist radar, Awa’awapuhi doesn’t get hammered like Kauai’s other top hikes.
For more details, and for  perfect-10 hikes you’ve never heard of, check out Kauai Trailblazer