It's a large city , with over 8 million people, and it's surprisingly diverse in its makeup, much like New York or Paris. It is the historical center of England, and has a rich and long history that has been remarkably well preserved. It is full of architectural marvels from Big Ben to Buckingham Palace, and museums chock full of art and history.
It is directly connected to Paris, France with the Chunnel - a high speed train that runs underneath the English Channel. It is a green city by modern standards, and has greatly reduced auto emissions by charging a heavy toll for driving into the city.
Libraries, double decker buses, Football passion (the British variety) and a ton of things to do for the traveler makes Britain a truly delightful country to visit.