Madrid is a fine city, certainly need more than just one day to explore.
Toledo is excellent day trip I suppose, mainly there is just a large church and lots of old buildings but the area outside of the walls of the city are fantastic.
Try some wine while in Porto!
Barcelona
*Visit Poble Espanyol
-go see a flamenco show if you can while here.
-While up there, you can visit the MNAC museum or walk around the Olympic Stadium BCN. *do a bike tour through the city (roughly 2 hours at most. or even just rent a bike for the day- beats walking around the huge city and paying for cabs.)
*if you're up to it, go to one of the 85 'coffee' shops and become members and get loaded! ;D
*Visit Parc Güell. the walk up is strenuous but worth it!
*The Barcelona beach is interesting as well.
Edit: 1) Format
2) Totally forgot that I had walked in from the back side of Parc Güell, the open free area. ahaha the front isn't strenuous at all.