Stingray City, Grand Cayman
The clear, shallow water of Grand Cayman's North Sound teems with southern stingrays. They began to congregate here because it's where fishermen cleaned their catch. Now, they come for handouts from tourists. Ebanks Watersports (345/925-5273 or ebankswatersports.com) offers trips to visit the sandbar, where passengers can touch, feed, and snorkel among these gentle swimmers. For more info, visit gocayman.ky.
Depoe Bay, Oregon
From now until June, Oregon's "whale-watching capital" welcomes roughly 18,000 gray whales en route to Alaska. Visit the Whale Watching Center in Depoe Bay to learn the best spots to view the grays. (Insider's tip: Northbound whales, which migrate now, swim closer to shore than southbound winter travelers.) Spring Whale Watch Week, when center volunteers will be stationed along the coast to provide viewing tips and facts, starts March 22. Or, for an up-close glimpse, hop aboard a Tradewinds Charters tour (800/445-8730 or tradewindscharters.com). For more info, visit whalespoken.org.
Assateague Island National Seashore, Virginia and Maryland
During spring and fall, this area's famed wild horses spend much of their time grazing the Virginia and Maryland coastlines. The best way to see the privately owned Virginia herd is aboard the Pony Express Nature Tour cruise. Captain Mark Coulbourne knows where the horses hang out (tours run May through October, 866/766-9794). On land, hike or bike the Chincoteague National Wildlife Refuge's 1½-mile Woodland Trail to an observation platform overlooking the ponies' habitat. For more info, visit nps.gov/asis.
Big Pine Key, Florida
This is the only place in the world to see the pint-size Key deer. A subspecies of Virginia white-tailed deer, they stand just 30 inches tall at the shoulder. Go to the National Key Deer Refuge in the early morning or at dusk for the best viewing―you may spot a newborn during the April-to-May fawning season. Stop at the visitor center before heading to an observation platform, or hike trails to see the deer. For more info, visit nationalkeydeer.fws.gov.
Many green sea turtles (or honu) that gather off Maui's shores eventually make their way to Maluaka Beach, also known as Turtle Town. To view the sea turtles in their natural habitat, grab your snorkel or scuba gear. Maui Eco Tours' Seafari claims an average of 15 turtle sightings per snorkel trip (866/891-2223 or mauiecotours.com). Sign up with Tropical Divers Maui for an introductory lesson with a guided dive (800/994-6284 or scubamaui.com). The Turtle Lagoon at the Maui Ocean Center offers a chance to see the reptiles and stay dry ( mauioceancenter.com).
Stonington Peninsula, Michigan
During August and September, thousands of monarch butterflies swarm Michigan's Stonington Peninsula on their long southern migration. You're likely to find many at Peninsula Point, a resting spot on the Upper Peninsula. Visitors can climb the 40-foot lighthouse for a bird's-eye view of the butterflies' journey across Lake Michigan, or observe them resting in the surrounding cedar trees. Pack a picnic, and don't forget a camera. For more information, call 800/533-4386 or visit travelbaysdenoc.com.
Delaware Bay, Delaware
Head here to visit one of the world's largest spawning grounds for horseshoe crabs. These crustaceans are protected at five community-based sanctuaries―Broadkill Beach, Slaughter Beach, Fowler Beach, Pickering Beach, and Kitts Hummock, all accessible to the public. There are also plans for a horseshoe-crab museum and research center in Milton (the only other museum of this kind is in Japan). You can help save the crab: If you see one turned on its back, "just flip 'em." For more information, visit horseshoecrab.org.
Mosquito Bay, Puerto Rico
Often called bio bay, this is one of the best places in the world to experience bioluminescence, a natural glow produced by living organisms. You can observe the glowing dinoflagellates (a type of microscopic algae) throughout the year, but the best time to visit is during a new moon when the night sky is darkest. Blue Caribe Kayaks in Esperanza leads educational expeditions and invites you to swim among the "stardust" (reservations are highly recommended); 787/741-2522 or bluecaribekayaks.com.
San Simeon, California
Winter is a great time to observe one of California's largest resident populations of elephant seals. Visit Friends of the Elephant Seal's Web site to learn about these funny-looking marine mammals and to get recommendations for the best places to find them. One top viewing spot: the Piedras Blancas rookery just north of San Simeon, where on-site docents will answer questions. For more information, call 805/924-1628 or visit elephantseal.org.
Knight Inlet, British Columbia
To see black bears and grizzlies, head to Knight Inlet, northwest of Vancouver. The Knight Inlet Lodge, open June through mid-October, offers three-, four-, and five-day packages. A boat takes guests to a channel brimming with salmon, and to other areas the bears frequent. For more information, call 877/764-4286 or visit knightinletlodge.com.