One would go tot Greenwich to experience the starting meridian; see the observatory building; walk in the park on a sunny day; shop for creative souvenirs at the Greenwich market; drink a beer at the Trafalgar tavern, which was once visited by Charles Dickens; visit the biggest maritime museum in the world; see Cutty Sark, the ship; or just walk around and enjoy the small-town atmosphere. I have indeed done some of these activities.
The maritime museum, which is the most equipped of its sort in the world, is an interesting stop for the children. My guidebook claimed that there was a clock from The Titanic in this building. However, this is not true. They do have a Titanic Hall, though. There are all kinds of ship models, equipment used in navigation throughout history, and special exhibitions for kids. Entrance is free, and it is open from 10am to 6pm in summer and 10am to 6pm in winter.
Greenwich Market is one of the most colorful markets I have ever seen, with creative clothing for babies and adults, handmade jewelry, natural soaps, and all other things behind the imagination of a common tourist. Once you have been there, you do not fall into the "My daughter has been to London and all she brought is this lousy T-shirt" cliché.
For me, a stop in the oldest pie shop in London was inevitable. They serve delicious shepherd pie against unbelievable low prices. After that, spoil yourself with an apple crumble served with custard. Lovely. I thought British food did not taste good, but Goddard’s pie shop did not disappoint me. I will never forget the simple but tasty meal here. It is located on Church Street; I do not know the number, but I am sure everyone around there does.
A visit to the observatory is a must when you are all the way in Greenwich. There is also an exhibition about discovery and possession of time by means of clocks through the British history. Entrance is free between 10am and 5pm.