EXUMA ISLANDS, Bahamas -- Picture yourself gliding through turquoise blue water, casually gawking at the stingrays and Crayola-colored fish skimming below, when suddenly the sandy bottom drops away, lurching into an indigo pit nearly 200 feet deep.

You’ve encountered a blue hole, a roughly circular, steep-walled ocean sinkhole that gets its name from the contrast between the dark blue of the deep and the lighter blue of the shallow surrounding area.

We’re hovering over just such a chasm in the Exuma Islands, a 120-mile chain of mostly uninhabited islands scattered by the sandy handful in the Bahamas. It’s one of many such blue holes that pockmark the Caribbean.

According to myth, dragonlike monsters lurk in the holes — some of which bottom out at 600 feet or more — occasionally grabbing swimmers by the ankle and slurping them into inky blackness. Thankfully, that doesn’t happen today, but as I hang over the dark gulch, I feel a tad untethered, like I’m drifting through outer space.

This is the last stop on a weeklong cruise aboard the Carib Dancer, a live-aboard dive boat based in Nassau. (If you don’t want to spend a week scuba diving, day excursions to the outer islands are also available through local dive shops.)

I haven’t had shoes on since I kicked off my sandals a week ago. In fact, I’ve barely showered. Who needs to, when you’re scuba diving four or five times a day and doing nothing but eating, reading and napping between dips?

I circle the outer rim of the sinkhole, checking under ledges and into crevices for interesting residents. The search turns up several lionfish, feathery-looking, cantaloupe-sized creatures that started showing up here about a decade ago. They’re not native, and since they were introduced (possibly in ship ballast, or when someone emptied an aquarium into the sea), they’ve proliferated. That’s not good news; lionfish compete for the same food as native species and crowd them out.

I kick back over the lip of the sinkhole and inspect a small coral head, where a snowflake eel has taken refuge. A menacing mouth full of tiny teeth gapes open, but that’s just how the slinky beast moves water over its gills.

I cruise into shallow water and poke my nose down in the turtle grass, where my sister points out a red, dinner plate-sized cushion star. Then I’m off again, mesmerized by the slow plodding of a conch. I’m so engrossed that I don’t realize a nurse shark, more like an oversized catfish than the star of Jaws, peers over my shoulder.

I snort into my scuba regulator, then paddle back to the edge of the blue hole. That’s when I see a 4-foot blacknose shark circling the perimeter. It takes one look at me, then dives like a missile back into the depths.

I head to the Carib Dancer, where, back on board, we swap stories.

This boat isn’t luxurious by any means. We’re sleeping on bunks in pint-sized cabins. The bathroom in our air-conditioned room is so small that you could take a shower while sitting on the toilet — and, in fact, my brother-in-law, who’s in the neighboring room, did just that when he bumped his shoulder into the faucet. Food is cooked up in a communal kitchen and is perfectly serviceable but far from gourmet.

In all, the boat can carry up to 14 passengers and five hard-working crew members. Live-aboards are always an adventure, and this week’s trip has been no different. The onboard machinery that mixes nitrox, a type of oxygen-enhanced air that some divers prefer, wasn’t working. And one night, the air conditioner went on the fritz, sending half the passengers outdoors to sleep under the stars on the deck.

We are here to dive, though, not to revel in luxury (although there is a hot tub on the sundeck, beer and wine in the refrigerator and hot cocoa after every night dive), and we’re having a blast.

Passengers pick up the Carib Dancer in Nassau, an hour’s flight from Miami or Fort Lauderdale. Once we left Atlantis resort in our rearview mirror, the scenery only got better.

Our best diving came in the Exuma Cays Land and Sea Park, a 176-square-mile marine park cut with underwater canyons and shifting sand bars. Wildlife is protected within park boundaries, and we noticed bigger and more fish there.

Among the sheer walls and lush coral reefs, we spotted angelfish crowned with gold, parrotfish scaled in green and purple, and bullet-shaped barracudas. I went nose-to-nose with a suitcase-sized grouper, stared down a dozen or more Caribbean reef sharks and sized up a lobster as big as a lawn mower.

After a week of such encounters, I’m still not ready to head back to dry land.

And I’m definitely not ready to slip back into shoes.

•  Information: www.dancerfleet.com