Go on a self-guided walking tour of the city of Porto.
I would absolutely suggest taking a port wine tour! This is a must as Porto is the port wine capital (or so they've self-proclaimed) but the value is phenomenal. The cellars are in Gaia, across the river, and there are extremely convenient bus pick-ups from easily accessible areas to take you up the winding hills to the cellars. I couldn't believe the price: I paid 3 Euros for a tour that lasted approximately an hour, with a tasting. I believe most all have English speaking tours and my cellar had English, Spanish, and Portuguese. I wish I had had time to do them all! There are quite a number of free tastings where you will get a couple of glasses.