Waimea Canyon State ParkThe 'Grand Canyon of the Pacific' — a 14-mile, 3,600-foot-deep gash of red rock and green ridges on western Kauaʻi

Mark Twain is often credited with calling this the 'Grand Canyon of the Pacific.' (He never visited Kauaʻi — the line is a tourist-board invention from the 1920s.) The geology is real enough though. Waimea Canyon was carved by two forces: catastrophic collapse along a fault on the west side of Kauaʻi roughly 4 million years ago, and steady erosion since then by the Waimea River, which still runs along the canyon floor. The iron-rich red walls and the moss-green ridge tops show up best after rain — and at 450 inches a year on the Mount Wai'ale'ale catchment above, rain is common.

Highway 550 (Waimea Canyon Drive) and Highway 552 (Kokeʻe Road) merge above the town of Waimea and run 19 miles up the canyon's east rim to a dead end at Puʻu O Kila over the Kalalau Valley. The two roads are slow — single-lane in places, with hairpins — but they put the four headline overlooks within a half-day's drive from anywhere on the island: Puʻu Ka Pele Lookout (waterfall view), Waimea Canyon Lookout (the postcard), Puʻu Hinahina Lookout (down-canyon to the coast), and the two Kokeʻe lookouts over Kalalau.

Trails drop off the rim at most mile markers. The Cliff and Canyon Trail (1.7 miles round trip from the Halemanu Valley road) gets you onto an exposed shelf below the lookouts; the Kukui Trail (5 miles round trip, 2,000-foot descent) runs all the way to the Waimea River. Black Pipe and Waipoʻo Falls are the two big trail destinations. Watch the weather above you, not just where you stand — a thunderstorm on Wai'ale'ale can flash-flood the canyon floor an hour later, and the Waimea River has killed hikers who didn't turn around in time.