Salamanca, often called the “Golden City” for the warm glow of its sandstone buildings, is a place where centuries of stories are etched into every wall. Visit its historic center to wander through cobbled streets lined with architectural marvels. The University of Salamanca, founded in 1218, is one of the oldest in Europe and still buzzes with student life.

This 2,000-year-old city, where the Teutonic Order founded one of its first commanderies in the 13th century, lies on the convergence of the Moselle and Rhine Rivers. Hop on a cable car, one of the city's most popular attractions, for stunning city-wide views, or cruise down the Rhine to spot some of Koblenz's magnificent fortresses and castles, including the Ehrenbreitstein Fortress and Schloss Stolzenfels.

One of the major rivers of the Iberian Peninsula, the Douro in north-central Spain and Portugal just might be the world's most beautiful wine region. Most of the river on the Spanish side isn't navigable, so river cruises generally travel roundtrip from Porto, on the coast of the Atlantic.

In Bremen's oldest quarter, the Schnoor district, little 15th and 16th century houses are lined up shoulder to shoulder. Found in its charming twisting lanes are artists' studios, goldsmiths' workshops and galleries. Past and present flow seamlessly together in Bremen. This is prominently demonstrated by delightful Böttcherstrasse - a unique, world-famous architectural ensemble.

Cardiff, the capital of Wales, is a city brimming with history, culture, and modern vibrancy. At the heart of its historic charm stands the Cardiff Castle, a magnificent structure that dates back to Roman times and has been a centerpiece of Welsh history for centuries. Explore the castle’s stunning medieval architecture and lavish interiors, or take a walk around the castle grounds, which offer picturesque views of the city skyline.