Kokee State Park, Mountains, Kalalau Valley, Waimea Canyon
Kokee State Park, Kauai.
Make sure you take along plenty of snacks, water and sunscreen and a camera. There is a concession in the state park, but pretty limited in what they offer. Also, the elevation gets up over 4000 feet (nearly 1500 meters) so bring a sweater too.
From Kaumualii highway in Waimea, turn mauka (toward the mountains) onto Waimea Canyon Drive. Feel free to stop anywhere along the way to take in the sights, but keep in mind that the locals go up and down these mountains daily and you should pull over when someone gets up behind you. Just pull over and wave, the folks appreciate it.