If you are docking at the Santa Apolonia area that the district of Alfama is right in front of your ship. Explore it by foot to get a sense for medieval Lisbon. It truly is one of the most charming districts of Europe. From the ship, simply cross the road and aim in an uphill direction.
Alfama is dotted with viewpoints. Keep your eyes open when you walk through this neighbourhood, you never quite know when the next best thing pops around the corner.