Balkan: building perfect marinas and hotels for tourists.

When Montenegro gained independence from Serbia in 2006, its then prime minister said, "Montenegro will become one of the most elite tourist destinations in the world... Better than St. Tropez." It was an ambitious statement, but after almost two decades, this small country nestled between Albania, Bosnia and Herzegovina, Kosovo, Serbia and Croatia is definitely on the way out. Taikuns now get the chance to sunbathe on giant superyachts off the coast, thanks to billions spent on glitzy yacht clubs and five-star hotels from some of the world's most exclusive chains that have sprung up along the beaches. The latest discovery is Mamula, a beautifully restored 19th-century fortress standing on its own island in the heart of one of the most beautiful stretches of the Mediterranean Sea.

We fly into Croatia to Dubrovnik and then drive south along a dusty road lined with tall cypress trees until we reach the border, where the landscape suddenly changes.

The towering Croatian mountains dip sharply toward the Adriatic, and small red-tiled towns huddle against the ocean's edge. Harriet Syme checks in at Hotel Mamula, one of the latest openings in Montenegro. The hotel, transformed from a 19th-century fortress, stands on its own island. There's an air of relaxed luxury here, Harriet says, and Mamula in particular has a "monastic sense of seclusion".

"Welcome to the Balkans," our muscular driver tells us with an ironic smile as we join the line of sounding cars.

There is only one border guard checking passports to enter and exit Montenegro. He checks three or four passports, looks at his phone, and moves to another lane. We wait only 20 minutes, but we are told that during the peak summer season the queue can take six hours.

Montenegro, a country no bigger than Yorkshire and with a population of just 620,000, is not part of the European Union, despite applying for membership in 2008. This is mainly due to the deepening political crisis that recently led to the resignation of the prime minister after 32 years in power.

A few minutes after crossing the border, we are dropped off at the entrance to Boku Kotor Bay, a fjord-like bay dating back to the 15th century, a UNESCO-listed site.

We board a boat and race across the sparkling Adriatic Sea, watching a cluster of villages stretch away.

The island of Mamula quickly comes into view. The soft, creamy curved lime walls of the fortress rise above rocky cliffs and the churning sea, with seagulls circling above.

On arrival, we are given a quick tour of the circular island - it is only 200 meters in diameter - then taken to our room. It's huge, with exposed stone walls and a vaulted ceiling, furnished in neutral wool and linen fabrics.

Although the hotel opened its doors in April, it's already busy with guests from around the world staying in one of 22 suites or ten rooms.

The atmosphere here is almost monastic in its seclusion. I often hear the phrase "polako" in Montenegro, which means to do things slowly and not be nervous.

The island is named after General Lazar Mamula, who built the fortress between 1851 and 1856 as part of an Austro-Hungarian fortification that formed a defensive line at the entrance to Boku Kotor Bay.

His past is controversial. The island was used by Mussolini's Italian prisoner of war camp during World War II before being abandoned and falling into disrepair. When Egyptian billionaire Samih Sawiris unveiled plans in 2015 to turn the ruined fortress into a five-star hotel, some locals opposed the idea.

Despite opposition, Sawiris secured a 49-year lease before embarking on a minimally invasive renovation project with monument protection authorities that took seven years.

Each brick moved was numbered so that it could be recovered and returned to the same spot, and each new structure could be removed at the end of the lease so that the island would remain exactly as it was found. I wasn't sure how I would feel if one of my relatives died here - tourists sipping champagne in the same building where people suffered.

But the island is not ashamed of its history and we are encouraged to visit the museum and memorial gallery on site. Every September, Remembrance Day is held to mark the date of the island's liberation from the Italians, and the families of those who lived here are invited to pay their respects.

Mamula is exactly the type of exclusive development the government hoped to attract the world's wealthiest people. Another such place is One & One day we were ferried on a vintage boat to Tapasake, a Japanese restaurant owned by One & Tennis player Novak Djokovic comes here every year, apparently crossing the border from his hometown in Serbia. Over glasses of creamy chablis, we consume portions of tuna sashimi, miniature avocado tacos and chicken tempura as the sun sets over the sparkling Adriatic.

Montenegro still retains its quiet appeal despite all this new money. One day we took a free boat from Mamula across the bay to the town of Herceg Novi, passing houses painted the color of the lemons growing in the orchards. We were dropped off at the Old Town harbor and watched cats sunbathing on the pavement and elderly fishermen working under their rusty boats.

A series of steep steps leads us through a maze of churches, small bars and Venetian-style stone villas with bottle-green shutters, and we arrive at a square where we order two glasses of local wine each in the shadow of a huge church. Price? Just £2.40 for each glass.

The Montenegrins are physically huge (they recently surpassed the Dutch to become the tallest nation in the world) and hope to become giants of tourism. Let the "paulaco" last.