Gray's Reef National Marine Sanctuary, graysreef.noaa.gov, (912) 598-2345
Roughly 20 miles off Sapelo Island, Georgia, this 17-mile piece of open ocean is home to a sandstone reef fat with corals, sponges, and fish, making it one of the most popular diving and sportfishing (grouper, black sea bass, snapper, mackerel) spots off the Georgia coast. Don't dive or fish? Visit the interpretive centers at the University of Georgia's Marine Education center and aquarium on Skidaway Island (www.uga.edu/aquarium, 912-598-2496) or the Taybee Island Marine Science Center (www.tybeemsc.org, 912-786-5917).

Gulf of the Farallones National Marine Sanctuary, farallones.noaa.gov, (415) 561-6622
Located northwest of San Francisco, this sanctuary abuts some of America's loveliest shore, offering beaches, wetlands, and great tide pooling (try duxbury reef tide pool for starters). The sanctuary is a breeding ground for harbor seals, elephant seals, pacific white-sided dolphins, and more than 300,000 seabirds. Whale-watching trips and nature expeditions head for the Farallon Islands, where they might spot gray, humpback, and blue whales, and, though outfitters won't guarantee it, possibly great white sharks near the islands, especially from September through November. More timid souls can visit the sanctuary visitor center at Crissy Field (near the Golden Gate Bridge, 415-561-6625).

Hawaiian Islands Humpback Whale National Marine Sanctuary, hawaiihumpbackwhale.noaa.gov, (808) 879-2818
Actually five marine protected areas, often with their own distinctive wildlife, this sanctuary includes the islands of Maui, Lanai, Kauai, Molokai, Oahu, and Hawaii. The recreational opportunities are myriad - kayaking, diving, snorkeling, sportfishing, and parasailing - but it's the humpback whales who steal the show, wintering amongst the islands (they journey down from Alaska) to mate and give birth. The best places to spot humpbacks are around the islands of Maui, Molokai, Hawaii, and Lanai from roughly October through May; the babies start appearing beside their mothers in January.

Monterey Bay National Marine Sanctuary, montereybay.noaa.gov, (831) 647-4201
The largest of the sanctuaries - 5,300 square miles, including 276 miles of shoreline stretching from north of San Francisco to south of San Simeon - Monterey Bay boasts one of the highest concentrations of marine mammals in the world. It's easy to play here: just drive along famed coastal Highway 1 and pull over wherever. Diving, surfing, boating, kayaking, fishing, whale watching, tide pooling (try point pinos lighthouse and point lobos reserve) - it's right at your fingertips.

Olympic Coast National Marine Sanctuary, olympiccoast.noaa.gov, (360) 457-6622
The sanctuary encompasses the waters and much of the shore along Washington's rugged Olympic Peninsula. Sportfishing charters abound (salmon, halibut, ling cod) - try Neah bay and La Push - and the beaches are stunning. There's also great tide pooling, and in the fall, winter, and spring, you can (with a license) dig up razor clams at low tide. The rocky reefs and lush kelp forests offer some of the best cold-water (expect an average temperature of 53 degrees) diving in the United­ States. Bird watching is first-rate, thanks to hundreds of offshore islands where seabirds such as puffins and common murres nest.