Many of the interesting sights around London (pics) are scattered across a wide area, mostly along the Thames, from Kensington on the West End to Canary Wharf in the East End. So you do have to be willing to get out and travel a bit. Fortunately, there are good transportation options, bus, underground and boat.
The top attraction in Portsmouth (pics) is the Historic Dockyard. This is a large collection of museums, artifacts and historic British warships. You could easily visit the dockyard everyday for a week and still not see it all. Perhaps the top highlight of the historic dockyard is the HMS Victory.