If glitzy Nassau and Freeport are the fast lanes of the Bahamas, then the 28 other inhabited cays known as the "Out Islands" are exit ramps to a spectacularly retro lane where the unspoiled tropical environment—scented with frangipani and aglow with tropical light—sets the pace.

It's a leisurely pace driven by diving, snorkeling, kayaking, and sport fishing—where time is measured not by the spin of a roulette wheel and the thumping rhythm of a "Jump," but by the accumulation of sand.

The Banks, a vast geological platform that rises from the South Atlantic, is shallow right up to the point where it isn't—such as at the "Tongue of the Ocean" where the drop-off into a mile's worth of blue oceanic water is marked by steep, plunging walls. Like walls elsewhere, the upwelling from the depths is the place to see giant pelagics—mantas, sharks, and even billfish.

But to say there are only 28 "Out Islands" is a bit misleading. For instance, the long and slender Exuma—home to the hemisphere's oldest marine park on 176 square miles of land—is actually a mini-chain of 364 cays and islets. Like the rest of the Bahamas, they are low and sand-covered slabs of limestone, dotted with coconut palms and low maritime scrub.

While the Out Islands all have fringing reefs, found in 30 to 90 feet of water, each seems to have distinguishing characteristics that set them apart. Andros sports some 400 blue holes—the best single collection in the wider Caribbean Basin—as well as a 120-mile long barrier-like reef. Harbor Island and nearby Eleuthera have their tongue-and-grove reefs as well as the 10 knot-per-hour Current Cut, a drift dive akin to flying with jet packs. Cat Island is spined with the highest point in the Bahamas—an ancient coral ridge almost 300 feet high—and a windward shore littered with Spanish colonial wrecks. San Salvador, on the far easterly rim of the Banks, has its legendary visibility. Southerly Long Island has its dependable Caribbean reef tip sharks. And the distant Cay Sal Banks—reachable only by live-aboard—has its own blue holes, sharks, and coral caves.

You can jet into Nassau and Freeport from many American cities, but it will take a smaller commuter—or the wonderfully time-stuck Mallard Sea Planes—to get you to the Out Islands. Look for all-inclusive dive-hotel packages as the best deals. A few resorts cater primarily to divers—such as the family-run Small Hope Bay on Andros. Prices range widely from fancy upscale resorts at $300 a night down to $75, depending on season and how much status you can afford. More serious divers might want to consider a live-aboard, such as the stable Nekton Pilot, which cruises all the way down to the Cay Sal banks, just north of Cuba.