"Like Mykonos, Delos was the island for VIPs," my guide tells me after we get off the ferry.

"It was the island of acceptance. Everyone was welcome - as long as they were wealthy!"

Despite being only about 3.5 square kilometres in size, Delos was described in antiquity as being "the greatest commercial centre of the whole world". As a free port, it attracted wealthy merchants, who brought in artists and builders to create lavish mansions decorated with frescoes and mosaics. Walking through the large archaeological site of what remains of this ancient city, it's clear that the temples, the theatre, and the propylaea would've been some of the most magnificent sights in the Aegean Sea.

Two millennia later, it's the sunbeds, nightclubs, and Instagrammable blue-domed churches that seem to be among the most popular sights for visitors to the Greek islands. But the heritage of the region should not be overlooked and a journey through the waters of the Aegean tells the story of the ebb and flow of some of the world's greatest civilisations.

I'm travelling on board the Celestyal Crystal for a week, one of two ships that Greece-specialists Celestyal Cruises use to show passengers the best of the country. At each port (and there are eight of them on this trip), you can choose to explore your own interests - perhaps a rural village in Crete, beaches in Milos, or an evening dinner in Santorini. And while I certainly find some time to swim, discover the local culture, and try some (ok, too much) ouzo, I'm also using much of my spare time to explore the ancient times.

The cruise begins in Athens, where the main historic sights are unavoidable. The hulking hill of the Acropolis looms large across the city, with the marble columns of its primary temple, the Parthenon, a beacon from any direction. The excellent Acropolis Museum next to it displays a large collection of artefacts from the site, but the most impressive section is the rectangle of columns marking out the exact size of the Parthenon, with original marble carvings positioned as they would've been on the temple, which can be seen through the full-length glass windows.

Standing at the top of the Acropolis, looking up at the striking facade of the Parthenon, you might think this is the most impressive of the ancient Greek temples. But this week's cruise takes me across the Aegean Sea to the ruins of Ephesus (which, although in Turkey, can be accessed by cruise passengers without going through immigration). It was here the Temple of Artemis once stood, more than four times the size of the Parthenon, one of the Seven Wonders of the Ancient World.

While the temple itself was eventually destroyed, much remains of this grand classical metropolis, founded by the Greeks then ruled by the Roman and then the Byzantine Empires. I slip slightly as I wander through Ephesus because even the streets are paved in marble, leading to temples, baths, and even brothels. The ornately decorated front of the library is one of the highlights, as is the huge theatre that still hosts concerts today.

It's not all ancient settlements, and even in Greece's bustling second-largest city, Thessaloniki, I discover the heritage that makes this one of the most underrated centres of the Mediterranean. Thessaloniki was one of the first bases for the spread of Christianity, with St Paul preaching here from 49 AD. Spread throughout the city, often on suburban blocks surrounded by apartment buildings, are some of the world's oldest churches, with stunning examples of early Christian art.

About 15 of these religious monuments, built from the 4th to the 15th centuries, have been declared a World Heritage Site and trace the evolution of worship through to the Byzantine period. They are all walking distance from each other and, as I visit as many as possible, my route leads me through pockets of local life, stumbling upon a baptism at one church, and a feast in the grounds of a monastery.

One of the selling points of Celestyal Cruises is that its smaller ships are able to get into ports that larger cruise lines can't access, and I get a firsthand example of this when we dock just metres away from the Medieval City of Rhodes. For about two centuries, from 1309, the Knights of St John transformed the island's capital into a monumental fortified city, with three layers of huge stone walls and a vast palace. It's still one of Europe's best preserved medieval cities and, although the main boulevards are now lined with shops and restaurants, it's easy to wander into the back streets to explore the dense neighbourhoods and discover the churches converted to mosques during the subsequent Ottoman period.

It's hard to condense thousands of years of history into a one-week trip - and even harder to recount it in just one story, yet somehow I feel pleasantly satisfied as the Celestyal Crystal pulls back into the port in Athens. I've travelled through ancient Greece, into the expansion of the Roman Empire, right up to the Ottoman Empire - with some detours through the Byzantine and medieval military eras. And I've done all of this while eating and drinking far more than I should have. I feel like a decadent man of the ancient world... who perhaps wouldn't be out of place in Delos all those millennia ago.

Michael Turtle was a guest of Celestyal Cruises. You can see more about visiting Delos on his Time Travel Turtle website.