SABA -- Halfway to a dramatic underwater spire called the Needle, I realize that only the fish can tell for sure which way is up and which is down.

Me? I’m floating in a universe of blue, about 60 feet below the waves. I see no ocean floor or rippling surface; I’m just a rubber-suited olive in an endless, undulating dirty martini of an ocean. Every now and then a translucent, pea-sized critter drifts past. Other than that, nothing.

I glance back, thankful that my husband is right behind me. At least I hope he is.

We kick a few more minutes into our watery dream and a dark form finally takes shape in the distance. It’s the Needle, and it rises from the depths to top out 80 feet below where our boat peacefully bobs under a cloud-streaked sky.

Saba is famous for these underwater pinnacles, formed by ancient volcanoes and laced with enough hidey holes and tuck-aways to conceal vast armies of eels, crabs and spiny lobsters.

We dip closer, dividing the jet stream of fish that’s swirling just over its surface: fat groupers with thick lips; plate-sized angel fish painted in iridescent blue and yellow; and aggressive little sergeant-majors that don’t seem to care that we’re hundreds of times as large as they are. The coral is lush; the sponges sway like palm trees in a hurricane.

We’re deep, though, nearly 100 feet down, and that means our time here is limited. We make two circles around the formation, then head slowly back to the mooring line of our boat.

We lug our equipment-laden bodies out of the sea, shrug off our buoyancy control vests and reach for the plate of fresh-baked chocolate chip cookies that miraculously appears before us.

We’ve come to the West Indies for a week aboard the Caribbean Explorer II, what’s called a “live-aboard” boat among scuba divers. We spend our days squirming into clingy wetsuits, strapping on bulky tanks of compressed air and pressing masks onto our faces until they form suction seals. Then we hop into the ocean, where we might get buffeted by waves, slurped by currents or stared at by 4-foot sharks.

To me, it’s heaven. Other folks might find it uncomfortable, tiring, less-than-luxurious or even scary.

This week is extra special because it’s my sister’s 50th birthday, and we’re doing what we do best to celebrate. That means plopping into the water four times a day, chugging around the coral reefs and lava formations, and checking out creatures so strange they look like they came from another planet.

Some of the weirdest have appeared at night, like the giant basket stars that unfurl their spindly arms along the metal walls of a sunken freighter called the River Taw, the victim of a 1985 hurricane.

Also on the strange and bizarre list? A courting pair of flying gurnards that swooped and twirled like underwater parrots; purple tube sponges clinging to an anchor chain like clusters of grapes; garishly colored slugs and snails creeping over coral branches; a bright yellow frogfish squatting on the ocean floor; and a nurse shark that went tooth to claw with a lobster. (The lobster got away in the end.)

This corner of the Caribbean has a rich history, too.

It was first settled thousands of years ago. After Christopher Columbus dropped by in 1493, word got back to Europe. It wasn’t long before the English, French and Spanish were fighting over its fertile grounds, where African slaves were set to work in sugar mills and on fruit plantations.

Evidence of those battles is easy to spot at one dive site off St. Kitts, within view of the Brimstone Hill Fortress. Dozens of anchors, some of them bigger than a man, are lodged in the coral, a reminder of a time when ships trying to beat a hasty escape from their enemies cut anchor and fled.

During our early November trip, the water wasn’t as clear as at other Caribbean destinations. The boat wasn’t as spacious or modern as some other live-aboards we’ve been on, either. Yet, we were here for the fish, not for the luxury accommodations.

And there’s not much that makes me happier than sitting on an open deck of a dive boat, swapping fish tales and stargazing after a full day of scuba diving.