If your honeymoon plans involve Kaua'i, a definite MUST-SEE is the Waimea Canyon State Park!!!
It's dubbed as the "Grand Canyon of the Pacific," by Mark Twain. Only...it's more lush, a lot smaller, and there's no river at the bottom, as the original. lol
Waimea Canyon is a large canyon, about ten miles long and up to 3,600 feet deep. Formed by erosion from the Waimea RIver, the canyon boasts a colorful array of red, brown and gren hues which are complimented by waterfalls and frequent rainbows.
There are two lookouts, the Puu ka Pele and Puu hinahina, both provide parking and provide breathtaking views.
There's even a local vendor that sells quick local grab-n-go snacks, i.e., dried mango, fried banana, dried papaya, to name a few.