Greenwich is located in south-east London and is the home of the Greenwich Meridian and Greenwich Mean Time. You've got plenty of historic buildings like the Royal Naval College and attractions such as the Cutty Sark and National Maritime Museum. You've also got the O2 stadium which has a shopping outlet, along with plenty of cafes and restaurants.
It's an up and coming area of London that's seeing more development of things to do and attractions, so it's definitly an area to check out if you have time.