Oahu

Concierge.com's insider take:

The diving isn't as spectacular around Oahu as it is off Hawaii's outer islands (the deep water isn't quite as clear here). But there are some terrific plane-wreck dives, including the sunken Beechcraft plane off Waianae, and the Corsair crash site off Hawaii Kai, where garden eels "sprout" from their holes in the ocean floor. For trips to these sites, as well as shore dives off the North Shore, contact Oahu Dive Center, the largest and most reputable operator on the island (808-263-7333; www.oahudivecenter.com).

Good snorkeling can be had off almost every Oahu beach; in particular, Sharks Cove and Kuilima Cove on the North Shore are great during the summer, when the water is calm (no worries—you're unlikely to see sharks). The best snorkeling spot by far, though, is Hanauma Bay Nature Preserve, a placid cove where the tropical fish have led protected lives since 1967. They're consequently tame as puppies, and swarm around snorkelers in hopes of getting a snack (feeding the fish isn't allowed, though obviously someone is doing it). It can be a little alarming to have hundreds of fish swooping in at you—and even nibbling at you—but they're harmless, and once you get used to it, it's actually pretty fun. There's a beautiful beach at Hanauma where you're welcome to spend the day, although you'll need to pay parking and entry fees (both under $5), and watch a short conservation film before you're allowed to walk down to the sand. The food at the sole snack stand is good but pricey (808-396-4229; www.co.honolulu.hi.us/parks/facility/hanaumabay).