see + do
Concierge.com's insider take:
Although Oahu is heavily populated (it has 800,000 people, or 80 percent of the state population), much of it is still undeveloped, lovely, and crisscrossed by safe, well-marked hiking trails. Of course, most tourists do the obvious hike up the 760-foot Diamond Head. The 1.4-mile, round-trip trek takes about 90 minutes and is pretty challenging for the average person, especially on a hot day, but the sweeping view of Waikiki is unbeatable. The trail starts at a clearly marked parking lot off Diamond Head Road; there are no facilities.
At Waimea Valley on the North Shore, hikes range from an easy meander through tropical gardens to a steep, .75-mile-long hike to a 40-foot waterfall. (You can swim at the falls when the water's high enough.) The valley is protected by Audubon Society gatekeepers, so you'll pay entry and parking fees to get in (Audubon Center, 808-638-9199; waimea.audubon.org). For other suggested hikes, check out the helpful Oahu hiking website www.backyardoahu.com.