San Lorenzo de El Escorial is home to the Monastery of El Escorial, a World Heritage site. This huge complex was built as a monument to commemorate the Spanish victory over the French in the battle of Saint Quentin. Construction lasted 21 years and when it was finished in 1584, the Monastery was the largest building in the world, with 24 km (14.9 mi) of corridors. The building includes a library, Kings' Courtyard, Basilica, and the Palace of Felipe II. The Kings' Pantheon is the burial place for most of the kings of Spain since Carlos I. The Monastery is decorated with works by the most prominent Italian and Spanish painters of the time. Look for works by Titian, Bosch, El Greco, and Velázquez, especially El Greco’s painting of "The Martyrdom of St. Maurice.”

Synagogues, mosques and churches stand together in Toledo's historic quarter, a testament to the medieval Spanish city's diverse history. The four towers of The Alcazar, a fortress built in 1085, dominate the skyline. Toledo and its surrounding countryside inspired El Greco, and his paintings are on display in many places around the city, including the museum that bears his name.

Encircled by some of the best-preserved defense walls in Europe, ancient Avila seems straight from the Castile region's medieval past. Nighttime illumination only adds to the allure of the turrets, fortified palaces, and cathedrals of this storybook World Heritage city.

Time seems to stand still in Evora, a well-preserved medieval town that features protective walls, a 13th-century cathedral, several palaces,and a 1st-century Roman temple. No surprise that the town center is a UNESCO World Heritage Site. Even though it’s kind of creepy, don’t miss the Chapel of Bones, where the remains of nuns and monks are arranged in a haunting mosaic.

"Aigues-Mortes" translates to "dead waters," but the salt marshes surrounding this mediaeval city actually have given this town one of its chief industries: sea-salt production. (Bring some home for epicurean friends.) Fortified into a Mediterranean port in the 12th century, Aigues-Mortes’ massive walls survive—walk along them for great views.

Amsterdam is truly a biker’s city, although pedaling along the labyrinthine streets can get a little chaotic. Stick to walking and you won’t be disappointed. The gentle canals make a perfect backdrop for exploring the Jordaan and Rembrandtplein square. Pop into the Red Light District if you must—if only so you can say you’ve been there. The Anne Frank House is one of the most moving experiences a traveller can have, and the Van Gogh Museum boasts a sensational collection of works.

Copenhagen is one of Europe’s oldest and most popular cities. It’s also one of the cleanest and most metropolitan. The dynamic Danish capital features progressive modern architecture, the must-visit Tivoli Gardens amusement park, stunning palaces, and all the activities and amenities you would expect in a world-class destination. Explore the canals and pretty narrow streets, appreciate beautiful old homes, and find great shopping and people watching on The Ströget.

Lefkada's name means "white," from the famous white cliffs of Cape Lefkata, site of an ancient temple of Apollo, where rumor has it that the celebrated Lesbian poet Sappho flung herself from the rocks. To stay with the mythology theme, don’t miss a boat tour on the mighty Odysseia, a colorful replica of a Greek war ship. You can also explore deserted monasteries in the mountains, splash around under the Nidri waterfalls and swim at some of Greece's most famous and beautiful beaches.