Billions are being spent on gleaming marinas and luxury hotels to transform tiny Montenegro into the St. Tropez of the Adriatic.

When Montenegro gained independence from Serbia in 2006, its then Prime Minister said: “Montenegro will become one of the most prestigious tourist destinations in the world… Better than Saint-Tropez.” »

It may be an ambitious statement, but almost two decades later, this small country – wedged between Albania, Bosnia and Herzegovina, Kosovo, Serbia and Croatia – is certainly on the right track. way.

Tycoons now sunbathe off shores on gigantic superyachts, the result of billions spent on gleaming marinas and five-star hotels from some of the world’s most exclusive chains that have sprung up along the beaches.

Its latest opening, Mamula, is a beautifully restored 19th-century fortress, set on its own little island in the heart of one of the most beautiful stretches of the Mediterranean.

We fly to Dubrovnik in Croatia, then travel half an hour south along a dusty road lined with tall cypress trees until we reach the border, where the landscape suddenly changes. Croatia’s rolling mountains rise to giant peaks that slope dramatically down to the Adriatic, and small terracotta-roofed towns line the ocean’s edge.

“Welcome to the Balkans,” our burly driver tells us with a wry smile as we join a line of beeping cars.

There is only one border guard who checks passports of cars entering and leaving Montenegro. He checks three or four passports before quickly scrolling through his phone and crossing the road to head back into the other lane. We only wait 20 minutes, but we’re told that in peak season the queue can take six hours to get through.

Montenegro, a country barely larger 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 a political crisis which is getting worse and which recently saw its Prime Minister ousted after 32 years. in power.

Just minutes after crossing the border, we are dropped off at the entrance to the Bay of Kotor, a 15th-century, UNESCO-listed fjord-like cove, where we board a speedboat and let’s cross the sparkling Adriatic while looking at the landscape. a group of villages extends behind.

Mamula Island quickly appears. The soft, creamy, curving limestone walls of the fortress rise from the craggy rocks and foamy sea, while seagulls circle above.

Upon arrival, we take a quick tour of the circular island – it’s only 200 meters in diameter – before being taken to our room. It’s huge, with exposed stone walls and a vaulted roof, and is adorned with neutral wools and linens.

Although its drawbridge was first abandoned in April, the hotel already welcomes guests from around the world staying in one of its 22 suites or ten rooms.

There is a feeling of almost monastic solitude here. A common expression heard in Montenegro is “polako”, which means take it slowly and don’t stress. This reflects the languorous and relaxed atmosphere. Most of our days are spent by the hanging pool in the center of the fort, or on the small beach, where the waves gently hit the white rocks and where the catamarans pass by.

The island takes its name from General Lazar Mamula, who built the fortress between 1851 and 1856 as part of the Austro-Hungarian fortifications forming a defensive line at the entrance to the Bay of Kotor.

His past is controversial. The island was used as an Italian prison camp by Mussolini during World War II before being abandoned and falling into disrepair. Some residents objected when Egyptian billionaire Samih Sawiris proposed in 2015 to turn the abandoned fortress into a five-star hotel.

Despite resistance, Sawiris was granted a 49-year lease before launching a minimally invasive reconstruction project alongside heritage authorities, which lasted seven years.

Each brick moved has been numbered so that it can be restored and replaced in exactly the same location, and each new structure can be removed at the end of the lease so that the island can be left exactly as it was found. I wasn’t sure how I would feel if a member of my family had met their end here – tourists sipping champagne in the same building where people were suffering.

But the island does not shy away from its history and we are encouraged to visit the on-site museum and memorial gallery. Every September, a Memorial Day is held to mark the date the island was liberated 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 biggest spenders.

Another is One & Only Portonovi, across the bay. One afternoon, a vintage speedboat transports us to Tapasake, One & Only’s Japanese restaurant, which has a swimming pool with sea views.

Tennis star Novak Djokovic comes here for a few weeks every year, probably crossing the border from his hometown in Serbia. While drinking glasses of creamy Chablis, we devour plates of tuna sashimi, avocado taco bites and chicken tempura as the sun sets over the sparkling Adriatic.

Montenegro seems to have retained its quiet charm, despite all these new investments. One day we take the free Mamula shuttle boat across the bay to the town of Herceg Novi, passing houses painted the color of the lemons growing in their gardens. We are dropped off at the old town port and watch cats sunbathing on the tarmac and elderly fishermen hammering away under their rusty boats.

A series of steep steps wind through the maze of churches, small bars and Venetian-style stone villas with bottle-green shutters, leading us to a square where we order two glasses of local wine in the shade of an imposing church. The price? Just £2.40 each.

The Montenegrins are physically immense (they recently overtook the Dutch to become the world’s tallest nation) and now hope to become tourism giants. Let’s just hope the “polako” lasts.