If you find yourself pressed with time.
Too bad you're afforded in this trip only a measly four hours in and for Lisbon. It's criminal I'd say on the part of the cruise ship. But, hey, one's got to make do of a given situation if only to stay ahead of the game. I'd suggests you decide on just a single itenerary to obtain the most out of your four hours. Your ship will very likely dock at the usual cruise line terminal at the Alcantara district in Lisbon which is halfway between the city center and the historic Belem district. All your nervous concern about distances, getting stuck in traffic, not to mention jostling with crowds at sights are rightly understandable. I agree keep it simple and let the thought of having missed the main attractions this time allow you to ponder a reasonable return trip to Lisbon. That said, pick either staying just right in Alcantara or the Belem district where you have the magnificent Mosteiro dos Jeronimos (Monastery of the Hieronymites), the Maritime Museum, a somewhat limited Archeological Museum next to the monastery and half a kilometer from here, the awesome Torre de Belem (Belem Tower). You can reach Belem on a quick and easy bus ride or the veritable tram (take #15)and you're there in less than ten minutes. At Belem, you'll be assured of giving your four hours more than its worth, tho I must warn you the throng of tourists will be there as well for sure to test your mettle. The other option already mentioned is to stick around in the Alcantara district. The neighborhood is right up the hill above the docks, you merely cross the train track and highway, climb the steps and you're in Alcantara. It's a quiet and very pleasant neighborhood, perfect for a slow unhampered stroll to peek around. You mention your own penchance for museums, one of Lisbon's (and quite possibly, the world's I must say)is the Museo de Arte Antiga (Museum of Antiquated Art, they really need to find a suitable name for this great place) which literally is just a few step climb from the docks. You won't miss it - it's a huge Victorian looking structure in royal yellow right next to the charming Jardim 9 de Avril (Garden of the 9th of April). The museum is filled with eclectic collection of Portuguese tapestries and 18th century Portuguese paintings, Oriental vases and furniture, faiences, sculptures, religious art and a marvelous collection of European paintings. Don't miss the museum's greatest acquisition - Bosch's triptych 'The Temptation of Saint Anthony'. The museum also has a wonderful cafe - Cafe D'Art - on its grounds set among giant jacarandas and literally jutting out the hillside overlooking the Tejo river where you can see and keep an eye on your ship. After your neighborhood ambling and museum tour, go have a meal or coffee/tea here where the kitchen serves outstanding Portuguese dishes. If you find yourself having extra time, a few doors away from the museum is The York House Hotel, one of Lisbon's grand old institutions with a memorable cafe to boot.