I used to think snorkeling and scuba diving would be terribly unsettling. What if I saw a shark? What if I didn't see a shark—and it bit me? I was sure I would panic in the open ocean, worried about what was behind or below me.

I couldn't have been more wrong. The first time I went snorkeling, I fell in love. It was so quiet—and so utterly peaceful—under the surface. Sunlight sparkled through the aquamarine water, showcasing the coral reef and its array of brilliant colors. Fiery orange fish mingled with magnificent red and purple fish swimming both alone and in schools. I watched, mesmerized, as a green sea turtle flapped his giant flippers and an eagle ray rose off the sandy bottom and undulated out to sea.

I had discovered a new world—a mysterious and beautiful world I never wanted to leave.

Of course, I had to leave. But whenever I'm lucky enough to take a tropical vacation to Mexico, Belize, or Costa Rica, the first thing I do is go snorkeling. If Denver had a coastline, I would snorkel every weekend. Unfortunately, we do not. But if I find myself itching to swim with the fish, I can do so—and for much cheaper than a weekend in Mexico—at the Downtown Aquarium.

In partnership with A-1 Scuba & Travel, the Downtown Aquarium offers special snorkel and dive programs in its Under the Sea exhibit. Snorkelers will have the rare chance to swim with a 400-pound Queensland grouper, a friendly sea turtle, moray eels, nurse sharks, red drums, and more than 400 other tropical fish and sea creatures without ever having to leave the Mile High City.

When I become certified to dive—this year, I hope—I can scuba Under the Sea or in the shark tank for an even more ambitious experience (think sand tiger sharks, brown sharks, zebra sharks, and barracuda). Every snorkel and dive adventure is led by certified guides from A-1 Scuba, and all gear is provided.

No experience is necessary to participate in the $75 snorkeling program. For $100 more, certified divers can scuba with either the fish or the sharks.

Tip: Bring a waterproof camera to capture your underwater experience on film, but note that there's a $15 fee.