The coolest, most overlooked places for a summer holiday in Europe

A passage to the sea in Rovinj, Croatia a fishing port known for its pastel-coloured townhouses and sweet swimming spots.

Globetrotters are always looking for new, under-the-radar travel destinations that provide a chance to escape the crowds and sea of selfie sticks.

As summer kicks off, Business Insider asked friends, colleagues, and some of the world's top travel experts for their favourite - and most overlooked - European destinations that can be seen in a long weekend.

From the mystical Arabic influence of Granada to the dilapidated charm of Porto and the gothic churches of Transylvania, here's a selection of their top recommendations, along with some local tips.

Pretend you're in a Bond film at the Bay of Kotor, Montenegro.

Montenegro provides a less obvious alternative to neighbouring Croatia, and it's not hard to see the draw of the stunning setting of the Bay of Kotor, with its glistening Adriatic sea and mountainous backdrop. The bay is also home to the preserved medieval old city of Kotor which just so happens to be a UNESCO World Heritage site.

One TripAdvisor user from the UK called it "Europe's best kept secret."

"Despite seeing many images of this place before my visit, nothing really prepared me for just how stunningly beautiful this bay is," the review stated. "The waterside setting (obviously) with its mountainous backdrop was for me a cross between the Norwegian fjords and those lovely Alpine lakes."

Admire the azulejos (painted tiles) and dilapidated charm of Porto, Portugal.

Emma McWhinney, the UK head of editorial at Secret Escapes, recommends a long weekend in Porto, a coastal city on Portugal's northern coast that's steadily growing in popularity as an alternative — possibly even a cheaper one — to Lisbon.

"Often overshadowed by bustling Lisbon, Porto, with its coastal thrills, postcard-perfect architecture, and eclectic culinary scene, is a must-visit cluster of colour and charm," she said.

Wander through Porto's hilly streets and admire the crumbling buildings and ramshackle colourful houses decorated with azulejos (painted tiles), and you'll soon see why its dilapidated charm is drawing in tourists.

Porto's proximity to some pretty stretches of beach adds to its appeal.

Soak up the Andalusian sunshine, snack on the famous free tapas, and lose yourself in a colourful maze of market stalls in Granada, Spain.

Granada, located in Spain's southern Andalusian region, is a city rich in history and culture —and its Arab influence gives it a mystical edge.

Aside from the tapas — it's one of the few places in Spain where a free tapa is religiously served with every drink — there's the majestic Alhambra Palace, abundant Arab baths that make a perfect first stop to unwind into your weekend, and the intriguing whitewashed gypsy caves of Sacromonte, where some of the city's best flamenco haunts lie.

Sakshi, a New York-based editor who recently visited the city, told Business Insider: "We enjoyed one free tapa with each drink. So we bar hopped as is recommended, we didn't ever get a second round at the same place."A tip for tourists is saying 'que tapa' after letting the bartender know the intention is a drink — either a cana (a small beer) or copa (little glass of wine). Bar Bodegas Castañeda came highly recommended and is somewhat of an institution. We started our bar hop there," she added.

Admire the sun-drenched domes and rooftops of the old town over sundowners in Cagliari, Sardinia.

While many flock to the glitz and glamour of northern Sardinia to enjoy the crystalline waters of the Costa Esmeralda, those wanting their money to go further should consider the south, specifically the island's capital of Cagliari, where I recently enjoyed a spectacular city break.

Perched on a hilltop, Cagliari's historic centre Castello provides the perfect spot from where to admire the sun-drenched domes and rooftops of the old town over sundowners.

After a long day of sightseeing, a particularly nice spot for an aperitif is the giant terrace at Caffè delle Arti which offers stunning panoramic views of the city and a good selection of craft beers the size of wine bottles.

The velvety local red wine, Cannonau, is not to be missed. Equally as enjoyable is the house red served chilled in jugs at restaurants — both slip down all too quickly.

Have an idle afternoon sunbathing on rocks or watching fishermen untangle their nets in Rovinj, Croatia.

Jess Cole, features editor for Lonely Planet magazine, picked Rovinj in Croatia as a perfect spot for a weekend break.

"With its piazzas, pastel-coloured townhouses, and elegant belltower, it's no surprise that the dignified Croatian town of Rovinj was once a subject of the Venetians," she said.

"Sights here are relatively few – the chief activity being myriad forms of relaxing by the sea. Idle away an afternoon by a quayside cafe watching fishermen untangle their nets, or stroll the cypress-shaded park of Zlatni Rt."