Barcelona contains both the authentically historic and the wildly bizarre. From the tree-lined Las Ramblas to the narrow alleys of Barri Gòtic; from the beachside nightclubs to the city's dozens of sacred churches and cathedrals, this city by the sea seems to attract all types: the family, the adventurer, the couple, the backpacker, the culture lover — and more — with an almost overwhelming variety of things to do. You could stay for a few days, but chances are you'll need a whole week to explore. In Barcelona, even the beach is bustling, but it's really the cosmopolitan city that gets all the attention. Much of the activity revolves around Las Ramblas, a series of narrow streets and alleys packed with restaurants, nightclubs and a vibrant pedestrian market. But you should also take a tour of Antoni Gaudí's masterpieces; Gaudí is responsible for sites like Parc Güell, Casa Batlló and La Sagrada Familia. And it would also be absurd to miss out on the eclectic shopping scene and the region's exquisite food and wine. Do you see why we suggest a week vacation?

PARIS

The City of Light draws millions of visitors every year with its unforgettable ambiance. Of course, the divine cuisine and vast art collections deserve some of the credit as well. The gentle River Seine rambles through the city, flanked by stately museums, centuries-old churches, and blocks of Rococo- and Neoclassic-design architecture, further enhanced by charming trees and glowing streetlamps. Peppering the Seine's cobbled walks and graceful bridges are impossibly chic Parisians, probably on their way to the market, cafe or cinema. Containing world-class museums, fashion, cuisine, and an atmosphere all its own, Paris is also a city of "many splendors," as Ernest Hemingway recalled in his memoir, "A Moveable Feast." Visit the Centre Pompidou, enjoy gourmet pastries, shop couture on the Champs Élysées or hit the boutiques in Les Halles, take in the view atop the Eiffel Tower, or even plan a day trip to Versailles Palace. But don't miss out on the simple pleasure of meandering the marvelous arrondissements (districts).

LONDON

The English writer Samuel Johnson famously said, "You find no man, at all intellectual, who is willing to leave London. No, Sir, when a man is tired of London, he is tired of life; for there is in London all that life can afford." More than two centuries have passed since Johnson's era, but his words still ring true. Life in London is invigorating, and travelers find that one visit isn't enough to experience everything this two-millennia-old city has to offer. Here, the antiquated clasps hands with the contemporary. You'll find the historic Tower of London and the avant-garde Tate Modern both considered must-sees. Shakespeare's sonnets are still being uttered by actors who don modern garb. Londoners most certainly still revere the royals, but they also rock out to Coldplay and Lily Allen. And while they still sip tea, they now drink Starbucks, too. A current leader in everything from politics and banking to fashion and music, London's culture compass is always attuned to what's next.