London has excellent public transportation options which are affordable and efficient. Consider getting an Oyster Card to save a bit more. A taxi or car hire will be more expensive but may be a better option if you're in a hurry or carrying luggage. Plan your journey using the Transport for London website or app.
If you have more time, visit the Natural History Museum and the Victoria and Albert Museum. For a night out on the town, catch a West End show or visit a comedy club. If you have less time, skip the National Gallery and do a Thames River cruise instead.
London has six airports; the main one is Heathrow Airport (LHR), located about 14 miles west of central London. Other options include Gatwick Airport (LGW), located about 30 miles south of London, and London City Airport (LCY), located in the Docklands, about 6 miles east of central London.