Churchill, Manitoba, Canada: Belugas
Once the ice breaks up in June, 3,000 Hudson Bay beluga whales head for the warmer waters of the Churchill River in Manitoba, their summer home. The whales' snow-white bodies glide through the saltwater like apparitions that seem inquisitive, even friendly. Slip over the side of a Sea North Tours Zodiac to greet them. Your arctic-rated wetsuit, hood, and cinched booties will keep you warm (enough) for a 30-minute or hour-long visit in early August. After the icy shock, your racing heart calms and you hear a pod in the distance whistling and chirping like canaries before eight or 10 whales appear, some within arm's reach. Sing to them through your snorkel, and they'll sing back.
Getting there: Take a direct flight to Winnipeg from Chicago, Minneapolis, Denver, Las Vegas, or Orlando, plus all major Canadian cities. There's no road to Churchill. You have to take the train (40 to 50 hours) or fly (two hours) from Winnipeg.
Mayan Riviera, Mexico: Cenotes
The Yucatan Peninsula might be known for coral reefs, but its most unique views through a mask are in the cenotes (seh-NOH-tays) beneath the Mayan jungle. The freshwater-filled sinkholes are like upturned mouths, some 2,000 of them, scattered around Playa del Carmen and beyond. Follow a guide down into the caverns connected by miles of beautifully illuminated subterranean rivers. At Hidden Worlds you kick through gurgling passages—so narrow your snorkel scrapes the stalactites above—that open onto massive rooms with jaw-dropping limestone formations. Young kids in tow? Paddle through a cenote on a Huck Finn-style raft at the nearby Xplor park.
Getting there: Fly into Cancun. By car, Hidden Worlds is an hour and a half south of Cancun and 35 minutes south of Playa del Carmen. Xplor is five minutes south of Playa del Carmen. Both parks run round-trip shuttle service from area hotels.
Rock Islands, Palau: Jellyfish Lake
There's a lake on Eil Malk island in the South Pacific where jellyfish reality is suspended. You can snorkel through swarms and not get stung. How? Over the millennia, the golden and moon jellies of Jellyfish Lake have completely lost their sting because they haven't had to ward off any predators. After a lifetime of dodging these free-swimming hazards, though, most snorkelers still feel nervous entering the water. The sheer volume of jellyfish, as far as the eye can see, is otherworldly. You quickly realize bumping into one (or 10) is unavoidable. When it actually happens, and doesn't hurt, the moment is surreal.
Getting there: Continental and United fly to Palau's Koror Island, where snorkel-tour operators offer trips to Jellyfish Lake, a 45-minute boat ride away. The remote lake is accessed by a short trail from the beach.
Grenada, West Indies: Underwater Museum
Usually, a sunken ship comes to mind when you picture an artificial reef. But in the reef just a few miles north of Grenada's capital, St. George's, a 65-piece sculpture garden sits on the ocean floor instead. Artist Jason deCaires Taylor created the Moliniere Bay underwater sculpture garden to help restore the bay's ecosystem a few years after Hurricane Ivan wiped it out in 2004. And it worked. Pink encrusting sponges now cover the face of a life-sized male statue like a mask. Little fish peck at growth on typewriter keys on the desk of The Lost Correspondent and swim between the wheels of another figure's bicycle. It's a fantastically bizarre parallel universe in shallow waters six to 26 feet below the surface. Let a guide help you see it all on a snorkel tour here or at Taylor's other underwater museum near Cancun.
Getting there: American Airlines flies direct from Miami, and Delta flies nonstop from JFK Airport in New York.
Campbell River, British Columbia, Canada: Salmon
Bob Hope, Goldie Hawn, and other celebs and heads of state have visited this Vancouver Island city with the intent of reeling in a scale-tipping Pacific salmon. But the Salmon Capital of the World's latest craze isn't snagging one of the thousands that return to the river each year to spawn. It's joining them. Yes, eye-to-eye, fin-to-fin with 70-pounders that look as big as you feel in the water. Wriggle into a wetsuit with Destiny River Adventures, and a guide will take you to hot spots where the fish hang out in pools at low tide. Jump in at high tide and you'll see fish blasting by you upstream. All five species of salmon show up at some point between July and October, with the best viewing in August and September.
Getting there: Take a ferry or float plane from Seattle to Victoria or from Vancouver to Nanaimo. By car, Campbell River is three and a half hours from Victoria and two hours from Nanaimo.