It's little wonder London is one of the world's top tourist destinations, attracting upward of 15 million visitors each year. Britain's capital city is a vibrant arts and entertainment center (its theaters are always busy), and 50 years after the Beatles, the country's music scene still rocks. London also offers one of the planet's greatest concentrations of cultural attractions. From royal palaces to the people's parliament, from museums and churches to riding a giant Ferris wheel for breathtaking views, you could spend endless days exploring London's sites without ever running out of unique things to see and do. An added bonus is that many of the most popular places to visit are free.