One of the world's largest sea fortresses, the 18th-century fort on Suomenlinna is a 15-minute ferry ride from Helsinki's Market Square (a mini-cruise that has lovely views of the city as a bonus attraction).

Displaying one of the most comprehensive collections of paintings in the world, the National Gallery is London's second-most visited museum

The Prado alone ranks with the world's top art museums for the riches of its collections

The spectacular Hofburg Palace in Vienna was for centuries the seat of Austria's monarchy, the powerful Habsburgs. Now the President conducts state business in the same rooms that once belonged to Emperor Joseph II.

The Royal Palace of Oslo was constructed at the beginning of the 19th century and was meant to be the residence of King Charles III who died before the work finished.

Prison, palace, treasure vault, observatory, and menagerie: the Tower of London has done it all and it's one of the top attractions in London.

The southwestern Finnish town of Turku, the country's oldest town and until 1812 its capital, lies on the Gulf of Bothnia, at the mouth of the Aurajoki River.

At the southern end of Argentina, Patagonia is famous for its spectacular landscapes: a dramatic mix of the Andes and long stretches of plains and plateaus. Most adventures here start in Ushuaia, the world's southernmost city.

The Vasa Museum (Vasamuseet) in Stockholm is Sweden's most popular museum and now attracts around a million visitors annually. More than 20 million people have visited since the museum opened in 1990, and it's not hard to see why.

This treasure trove of classical and historical artwork has been built up over many centuries by various popes and includes some of the most important pieces of artwork in the world.