Bracing against the wind on an exposed bluff 140 feet above the sea, my older sister Erin and I feel as though we're diving. We're on no ordinary trail; this one traverses piles of ancient coral. Their calcium-carbonate exoskeletons are razor-sharp, each polyp of star and brain coral an exact replica of those found in the underwater kingdoms we love to explore. I've seen examples of these fossils in curio cabinets at aquariums and natural history museums. But here, on the crest of Cayman Brac, they lay beneath our hiking-shoe-clad feet, out of place - like stumbling upon a giant live oak in the middle of the Mojave Desert.

I creep toward the edge for a closer look at the nesting boobies near the cliff's edge. The enormous brown birds have found their home here for centuries: Cayman Brac settlers first created this trail in the 18th century to collect booby eggs. Erin shouts out, "Sister. Stop!" I do, appearing obedient. But in truth, the sensation of falling had surged through me the moment I'd caught sight down the cliff of the waves crashing against its base. I scramble back towards Erin and we continue down the coral trail, imagining a time when this very place was submerged, when it may have resembled the incredible walls we've been diving on all week in the Bloody Bay Marine Park in the Brac's little sister, neighboring Little Cayman.

When I heard the term Sister Islands, used to refer to Little Cayman and Cayman Brac -- the tiny nature-based gems 90 miles east of the diver's mecca Grand Cayman -- I knew I had to take Erin there with me. After all, it was she who got me started diving, and together we share many traveling memories: Turning cartwheels down the mysterious underwater Bimini Road, believed by some to be the lost road to Atlantis; me searching for her, last seen in a bikini and sarong in a Portuguese fishing village at 3 a.m.; and most recently, diving with our newly-certified Mom in Belize.

But I fear that's all about to end. In a few months Erin will remarry, resulting in a blended family with three children. Commitments will be re-prioritized: Sister (that's me) will fall down the list. 'Tis life, I understand. So while most people celebrate a final hurrah amidst Vegas-like hedonism, Erin and I looked to the Sister Islands -- Little Cayman's legendary walls and Cayman Brac's natural beauty -- to affirm our own friendship and to help keep us close as life changes.

Diving In
For me, the name Mixing Bowl conjures many images (cookie dough, for instance). But in Bloody Bay Marine Park it is the legendary site where swim-through-friendly Jackson Wall with its Swiss-cheese-like substrate meets the skyscraper-sheer Bloody Bay Wall. And if it sounds cool to divers, for some reason it's even more interesting to the marine life that schools at this intersection of topographical contrasts. As it turns out, this and all the rest of my favorite dives are within half-a-dozen moorings of each other: Marylin's Cut, Dottie's Delight, Randy's Gazebo, Lili's. The names are to divers what the Social Registry is to blue bloods. By day three with Reef Divers I'm certain that this is among the best diving in the Caribbean.

Mixing Bowl is in one of the shallowest sections of Bloody Bay Wall. Erin and I translate that to mean one thing, extended bottom time, and we are keen to explore. This site is a fun house and the options endless: Erin waits for me at the end of one sand-chute swim-through, and as we start back through another, we discover the passage filled by an enormous sleeping nurse shark. One moment we're watching a hawksbill turtle perform its graceful dance; the next a reef shark flies towards us from the shallows and then sails overhead, disappearing into the blue. Grouper line up at cleaning stations and a secretary blenny catches my eye -- and my extended attention -- on a coral head out on the wall.

As soon as we emerge from the water, all we can talk about is getting back in. Erin and I agree that we could dive Mixing Bowl everyday and never get bored, though frankly, it's always been Erin who brings playfulness and joy to each underwater discovery. I could dive anywhere with her and never get bored.