Our small boat bobbed in the clear blue waters of the Aegean Sea, anchored near a rocky uninhabited spit of land. In the distance, the white cityscape of Fira, Santorini, glistened against high seaside cliffs. I shinnied down the ladder into the sapphire sea. A few minutes later, my party of 10 was swimming toward an otherworldly lagoon. Its dark yellow color, sulfuric scent, and hot springs were the products of volcanic activity below. In the shallows, we wiped the iron-rich mud on our faces.

All part of our mega-cruise-ship adventure. Sort of.

While most of our fellow passengers from the Celebrity Constellation were sitting at cafes or shopping on Santorini, where the ship had docked, my wife and I took a different approach to a shore excursion. We joined only four other couples on a private boat tour to explore off-the-beaten-path spots.

A few years ago, my images of large cruise ships were of buffet lines, regimented schedules, and herd mentality. I was, frankly, uninterested.

No more. I've learned that cruises can afford singular adventures away from the crowds. It is even possible to style a mega-liner cruise to fit almost any image you have of a dream vacation. It just takes a bit of precruise research.

My wife, Margie, and I returned this summer from our third Mediterranean cruise, all on ships of about 3,000 people. Perhaps our most important piece of knowledge drawn from them is this: There is a wealth of wonderful onshore experiences beyond the excursions the cruise line offers.

Ship offerings can be expensive, and many require you to board a bus and, upon reaching the destination, follow a sign-carrying tour guide.

Some ship tours are just fine, maybe even advisable for first-time visitors to a foreign place. We were much more inclined to take ship tours on our initial Mediterranean trip, and we have no regrets about spending an afternoon in Pompeii, or touring the ancient city of Ephesus, or taking a rather lengthy bus trip to Florence on cruise excursions. In Athens, we relished the Acropolis tour leader who pointed to lemon trees, saying the fruit was lousy in taste, but fine for throwing at local police and politicians.

Nonetheless, our most memorable experiences have come when we either ventured off on our own or happened upon a private tour, by planning or by chance.

How did we wind up swimming in hot springs off a volcanic island during the stop at Santorini? It was mostly serendipity - and my wife's adventurous nature.

On the train ride from Rome, where we'd landed, to Citavechii, the ship's departure port, we rode with a couple named Tom and Sherry from Orlando, Fla. After the cruise got underway, we met an English farming couple, David and Fiona, who told us Tom and Sherry were looking for two more people to fill out a 10-person small-boat tour in Santorini. We sent word that we'd love to take those two spots.

Santorini itself is a jewel of the Greek islands, with whitewashed houses set into seaside cliffs. Add swimming, and you're talking dream vacation.

I'd venture that most of the ship's passengers spent their day in either Fira or neighboring Oia, jostling with hundreds of tourists from the several cruise ships that dotted the port. For those who love shopping - the standard fare being jewelry, clothing, and trinkets - six hours in Fira, with a coffee or wine break, can be lovely. But way too predictable.

While the majority of the passengers were deciding which of three ways to get to the top of Fira - donkey ride, walking the same donkey path while dodging the inevitable donkey droppings, or cable car - we were picked up by a small Greek fishing boat run by Capt. Stathis of Amenos Santorini Sea Trips and dropped at a tiny harbor on Santorini. Included in the price of $80 per couple was a round-trip bus journey to Oia, at the top of the island, where we had two hours of on-our-own shore time. Time enough for trinkets and coffee.

When we returned to the harbor, Capt. Stathis took us for our swim and then to a tiny church on the other side of the island.

When we reflected on this cruise, Margie and I immediately agreed the stop in Santorini was our favorite, with Naples No. 2.

What made Naples rival Santorini for memories? Another private tour, which Margie found on the website Cruisecritic, a tremendous resource for information about cruise ships and excursions, both private and ship offerings.

This tour was organized by a delightful Florida retiree named Nancy, whose sardonic personality found a soul mate in the guide, Anthony, who also drove the eight-passenger van. The van took us down the windy, steep cliffs of the Amalfi Coast, the scenery and vertical drops leaving all of us breathless.

The trip ended in the postcard-beautiful town of Positano, where we had 90 minutes on our own. My wife and I headed to a beach favored by locals, buying a bargain beach towel and diving in for another Mediterranean swim.

The out-of-the-way spot and sparkling water reminded me of another time when Margie and I departed from the norm. On our first trip to Santorini on an earlier cruise, Margie researched a local swimming hole. We took a city bus from Fira, made our way down a cliff to a tiny fishing village, and hiked a half-mile along the coast, where two dozen people were diving from cliffs or lowering themselves into a swimming hole carved between rock formations. Most of the swimmers were covered in tattoos, but we were happily accepted.

You won't find that swimming hole in any of the ship's tour offerings.