Think of a mountainous, moon-shaped island about 8 miles wide. Then imagine the island shaped like a crescent, with its whole left side gone. Some 3,600 years ago, that's what happened to the Minoan island of Thera when a giant volcano blew its lid right through that dot in the Aegean Sea.
Seawater filled the gap left by the blast, creating a lagoon about twice the size of the Las Vegas strip. Sheared off by the explosion, cliffs a thousand feet high were left edging three sides of the lagoon.
Geologists say the eruption created a tsunami wave that was so big - perhaps the height of a 16-story building - that it wiped out large areas of Crete (70 miles away) and went on to tear up the beaches at spots as far away as the Israeli coast.
Fast forward to today, and the island of Thera, now Santorini, is again triggering tsunamis. Only now they're headed the other way, bringing tidal waves of tourists to the island on planes, cruise ships and water ferries.
The bulk of Santorini's visitors arrive on a small navy of ferry boats and high-speed catamarans from Greece's main port at Piraeus 130 miles away. About a half hour from the island, passengers start doing double-takes as Santorini's snow capped cliffs come into view. Snow capped? As you get closer in, the snow turns into hundreds of whitewashed buildings running down the hillsides, seemingly built on top of each other.
A cable car near the dock area whisks visitors up the cliffs to the island's main city at Fira in just a few minutes. Or you can walk up 588 steep, zig-zagging steps. Or ride up the steps on donkeys. A tip: Take the cable car.
During the summer it's not unusual to see cruise ships anchored all over the lagoon while regularly scheduled jet flights from Athens (about a 40-minute hop) zip overhead to the Santorini airport. On peak travel days the scheduled flights are joined by charter jets from all over Europe.
Little did the ancient Minoans know that their big blast would some day create big-time tourism.
Today, looking down at the lagoon's bluer-than-blue waters from atop the cliffs at Fira, you get the feeling you're on another planet - if you can ignore the mobs of tourists meandering around.
Winding through the city are narrow lanes lined by wall-to-wall shops offering exquisite jewelry, hand-woven clothing and world-class tchotchkes. You'll also find plenty of bars and outdoor restaurants up there, typically with views of the 8-mile-long lagoon. The better the view, the steeper the prices.
There's one time of the day when patrons are willing to pay just about anything for an outside seat at Fira or the nearby town of Oia: at sunset, when spectacular, sherbet-colored skies fill the heavens over the lagoon and as far as you can see beyond that.
History buffs can opt for a tour of the 40-mile-long island on buses leaving from the dock area. Along the way, guides point out remains of the days when Santorini was a colony of the Minoans, then of the Greeks, Phoenicians, Romans, Byzantines, Franks, Venetians (who named the island Santorini after Saint Irene) and the Turks. Santorini hooked up with Greece again in 1912.
The bus tours end in a hair-raising drive up the narrow, winding mountain roads to Fira (from which most tourists take the cable car back down to the docks).
Staying there: Visitors have a choice of 180 or so tourist-class places to bed down around the island. They range from upscale hotels with stunning views of the lagoon such as the hillside Iconic Santorini to older, view-less inns for as little as $50 a night.