To visit Agrigento's old town you need an half day time, a comfortable pair of shoes and an open and inquisitive mind.
Park your car in the closest parking to via Atenea, the gateaway to your tour. Leave aside guide books and maps: you will never get one enough detailed about the crazy, entangled subcession of "cortili" and "vicoli" (courts and lanes of arabic origins). Instead of map consulting try to take the best of the poor but enthusiastic english spoken by locals.
Don't give up at the sight of the 110 steps that separate via Atenea from Santo Spirito cloister and go for it. The surprise of an enchanting gothic monastery (XIII century) will reward your efforts. And the convent home made almond cakes will return to you more than the calories you burned.
Go straight up. Look for the norman Cathedral. Don't care about people warning about it possibly being closed. Its severe and imposing fassade deserves a visit. And please pay attention to the several baroque fassades that you will meet on the way to the Cathedral: Palazzo Del Carretto, Celauro, Borsellino, Xerri, Casa Filippazzo...splendid fanthoms of a noble life, gone for ever.
Explore the crypt and the basement of Santa Maria dei Greci church. You'll find out a greek temple in the underground. A temple still supporting a different faith, but a faith, anyway.
And then start finally to go down the steps: hundreds of steps, up to plunge in the most arabic quarter of the town, the "Rabatu". Smell its spicy odours, listen to the voices in the houses (always too loud to be ignored) smile at the children asking you "Yu spiiik inglish?". Stop and look at the faces of people. You will see a lot of Tunisian and Moroccan faces...Araby is back! Araby has never left here.
Now turn your eyes southwards, on the brilliant blue of the Mediterrean and you will suddenly realize how close Africa is.