Or, you can go to the Georgia Aquarium in Atlanta, the Florida Aquarium in Tampa, or New Jersey’s Adventure Aquarium in Camden, where you can leave the Dramamine behind and swim in gin-clear water with everything from whale sharks to a 400-pound grouper. Fly to Fiji, and you could catch the distant, hazy flicker of a sinuous blue shark. Slip into Denver’s Downtown Aquarium’s nearly 400,000-gallon Sunken Shipwreck exhibit, and be prepared for something far more intimate.

“The great advantage that aquarium diving has over the real world is that it guarantees you’ll see animals,” sums up Todd Hall, the Downtown Aquarium’s dive-safety officer. “When you dive in our shark exhibit, you’re going to see three 12-foot sawfish and five sand tiger sharks up close and in your face. They’re not bashful. It’s their house.”

Hall and a group of like-minded divers launched the Downtown Aquarium’s program in June 2007. Since then, more than 6,000 divers and snorkelers have swum on the other side of the 12-inch-thick acrylic wall. The aquarium partners with Denver dive operator A-1 Scuba & Travel Center. Divers and snorkelers (by Hall’s guesstimates, roughly two-thirds of their guests are snorkelers) sign up with the dive shop, which oversees both the snorkeling and the dives. For divers, $175 buys one dive, in either the Aquarium’s 200,000-gallon Under the Sea exhibit or in the vast Sunken Shipwreck exhibit. Snorkelers fin through the Under the Sea exhibit ($75) alongside nurse sharks, moray eels, a green turtle, several hundred fish, and more than 40 other forms of sea life.

For divers, the Sunken Shipwreck exhibit is the pièce de résistance, a communion with an impossible cast. The surreal sawfish (imagine a shark that has hedge trimmers for a nose), which is normally found in Australia; zebra sharks, which inhabit the Western Pacific; and sand tiger sharks, found primarily off the North Carolina coast. It’s a bit like getting Elvis and Justin Timberlake in the same room.

“It’s a unique twist,” says Shane Taylor, A-1 Scuba’s general manager. “You’ve got a collection of animals that you’re never going to see together anywhere in the world.”

It’s a hoot for folks on both sides of the acrylic.