I think London is the greatest city on Earth. It has more UNESCO World Heritage Sites than any other city in the world. In a 2007 worldwide poll, London was voted the second-most beautiful city in the world in terms of architecture after Sydney, Australia.
But the actual most beautiful city in the world has to be Bath in Somerset in south west England, with its wealth of beautiful Georgian and Roman architecture and statues. It's also got the ancient spa baths (where the city gets its name) built by the Romans over a giant natural spring, and people have bathed in them for centuries. The Romans called the city Aquae Sulis ("the waters of Sulis").

The Great Bath at the Roman Baths in the city of Bath was built by the Romans. The nearby temple was built between 60AD and 70AD. The baths contain warm water as they were built over a natural spring and, up until the 19th century, people would bathe in the water.

The Royal Crescent, Bath