Frommers site has a couple of maps & suggested walking tours. Those may help you decide, Wendy. Cheers, Anne
http://www.frommers.com/destinations/lisbon/54_maps.html

I took the following from the site www.europeportreviews.com

Where does the ship dock?

Ships dock at the port of Lisbon close to the downtown area and about 4 miles from the old section of Lisbon. The ship is also quite close to the Lisbon International airport (about 15 euro by taxi) for those either embarking or debarking in Lisbon.