Seen from the train, Durham presents a magnificent sight, with cathedral and castle perched atop a bluff enclosed by a loop of the River Wera, and linked to the suburbs by a series of sturdy bridges.

The Main River winds through the heart of Germany, offering a scenic journey through picturesque towns, rolling vineyards, and historic cities.

More than 300 days of sunshine annually (more than San Diego or Miami Beach) earns Denver high marks with visitors and make sunglasses a must. For the city's most energetic shopping, dining and entertainment spots, point your compass in the direction of Larimer Square, the Tivoli, LoDo and the 16th Street Mall.

If you find yourself in Rotterdam, there's a strong chance you've arrived by water. This popular port city (the second largest in the Netherlands) has gone through an architectural renaissance since World War II, with daring, innovative structures dotting the city (cube houses!) and defining its skyline. Café culture is on the rise here, so grab yourself a table and a cup.

Southeast Spain's seaport of Cartagena is a large naval base on the Mediterranean coast. The city was founded in 220 B.C. and boasts Roman ruins, mosaics and murals.