How to explore Greece's lesser-known islands like a local

A perennial favorite among holidaymakers, Greece consistently ranks among the top 10 vacation destinations in Europe.

But now it wants tourists to get to know lesser-known locations across its thousands of sprawling islands.

"We're moving beyond sea and sun. We want to prolong the tourism season in both time and space," Olympia Anastasopoulou, secretary-general for tourism policy and development at Greece's Ministry of Tourism, told CNBC Travel.

For that, the country is investing in its more remote locations, including Syros, Amorgos and Milos, as part of its "All you want is Greece" campaign.

To ease overtourism, popular hot spots such as Mykonos and Santorini are being repositioned as shoulder season destinations.

"It's our goal for those islands to expand more in seasonality, too. We would like it for the tourism flows to be expanded in other months," said Eleni Mitraki, director of tourism promotion at the Greek National Tourism Organization, noting the season could run March through November.

The plans coincide with the expansion of direct flights from the United States to Greece in March 2023.

Currently, Germany and the U.K. represent Greece's largest inbound tourism markets by revenue, followed by the United States, France and Italy. However, Anastasopoulou said further growth from other markets, most notably Canada and India, is expected.

Here are CNBC Travel's top picks to get you off the beaten track in Greece.

Rock climbers' paradise

Located within Greece's Dodecanese island chain in the southeastern Aegean Sea, Kalymnos is famous for its sponge-diving — underwater diving to collect natural sponges from the seabed — which brought considerable wealth and recognition to the island in the previous century.

More recently, the island has become a world-renowned location for rock climbers, with more than 3,000 climbing routes spanning the numerous crags, caves and overhangs of its rugged landscape.

Kalymnos' tourism season peaks in the fall with the Kalymnos Climbing Festival, which takes place most years. But adventure junkies can get their kicks year-round, with a host of other activities including scuba diving, hiking and boating.

How to get there: Kalymnos can be easily reached by boat from nearby Kos, with crossings taking 45 minutes by ferry and 25 minutes by speedboat. It's also accessible by plane from Athens. 

Haven for history buffs

Ios, also known as Io or Nio, is located between Santorini and Naxos, and was once seen exclusively as a party destination. But the Cyclades island has revamped its image over recent years to embrace its historical and natural attributes.

Home to one of Greece's most ancient archaeological settlements, the Skarkos monument, Ios also boasts a strong connection to the Greek epic poet, Homer, who is said to have favored the island and, potentially, ended his days there.

Alongside history, visitors to Ios can also explore its plentiful beaches, and hiking and diving spots, before tucking into some of the local cheeses for which the island is famed.

How to get there: There is no airport in Ios. The island can be accessed by ferry or speedboat from both Athens and the other Cyclades islands. It can also be reached by helicopter from Santorini.

Movie lovers' delight

Skopelos became famous as the filming location for the hit musical rom-com "Mamma Mia," and has since emerged as a popular destination for weddings, honeymoons and movie tours.

Part of the Skopelos archipelago in the northwest Aegean Sea, the island combines stunning beaches and picturesque villages with a host of diving, yachting and cycling routes.

Legend has it the island was founded by the son of the Greek god of wine. And though many of its vineyards were destroyed by pests in the 1940s, small-scale, domestic production continues to this day. Meanwhile, natively grown plums, almonds, chestnuts, figs, citrus fruits, olives adorn the local cuisine.

How to get there: Skopelos is reachable by ferry or speedboat from the port city of Volos on Greece's mainland. Services run year-round, with additional routes from other islands added in high season.

Hiking retreat

One of biggest islands of the Cyclades and just two hours from the Greek mainland, mountainous Andros has a varied landscape of forests, waterfalls, beaches and local vegetation, making it ideal for an outdoor escape.

Visitors can explore the island via its large network of hiking trails, or try their hand at windsurfing or scuba diving, before sampling the local cuisine.

Arts and culture fans can check out Andros' collection of monasteries, galleries and museums, including the Archaeological Museum of Andros and the Museum of Contemporary Art.

How to get there: There is no airport in Andros. The island can be reached by ferry from Rafina port on the outskirts of Athens.

Isle of innovation

One of the Dodecanese islands, Astypalea has a rich ancient history. But it is positioning itself firmly in the 21st century with the goal of becoming the first sustainable and smart island of the Mediterranean sea.

As part of a deal with the Greek government and Volkswagen, Astypalea plans to implement islandwide, zero-emission mobility by 2030, with traditional vehicle rentals to be replaced with electric cars, e-scooters and e-bikes. Elsewhere, charging points and renewable energy sources will also be added.

Tourists arriving on the so-called Butterfly Island can also enjoy its natural landscape, home to beautiful beaches, rocky hillsides and diverse flora and fauna, as well as its picturesque villages of bougainvillea-clad white houses.

How to get there: Astypalea is accessible from Athens by both ferry and plane.

Island-hopping

Surrounded by a necklace of 24 islets with dozens of blue-green beaches, Lipsi in the Dodecanese is considered the Polynesia of the Aegean Sea and an eco-paradise.

With a rich expanse of flora and fauna protected by the European Union, the island is home to diverse wildlife, including Mediterranean monk seals and sea turtles. Dolphins are also common in the area, and a new Aegean Marine Life Sanctuary for dolphins is set to open soon on the island.

Holidaymakers can enjoy days spent boating, diving, beach-dwelling and hiking, before tucking into seafood dishes and experiencing local festivals, such as August's wine celebration.

How to get there: Lipsi is only accessible by ferry or speed boat, with regular services running from Athens and Leros.

Divers' delight

Alonissos, part of the Sporades group of islands, is a diver's paradise and the site of Greece's first underwater museum. Featuring "Parthenon of the Wrecks," one of the biggest Classical-era shipwrecks dating back to 425 B.C., the site offers recreational divers a unique insight into the region's history.

The island is also home to the National Marine park of Alonissos and Northern Sporades, currently Europe's largest marine protected area, giving visitors the opportunity to see a vast array of plants and animals.

Kayaking, hiking and cycling are among the other activities available on the island, while museums and a local theater group showcase the island's arts and culture scene.

How to get there: Alonissos can be accessed either by plane or by ferry from the ports of Volos, Agios Konstantinos and Kimi.