A wonderful place to visit with the Theater District and all of the historical sites such as the Tower of London, and so many other sites you can spend days just touring the city. Much of it can be done on foot but riding the Tube is one of the easiest ways to get around town. This underground system is cheap to ride and goes almost every where. Not so inclined cabs are great and readily available, or maybe a double decker bus.
London is a great place to base as you tour the rest of the country by rail. With high speed trains and relatively low fares.