Mario's place is perfect: location is ideal, in the middle of everything, walking distance to the Douro (about 10 min) , to the caves (about 15 min). Also the place is very quiet, the room is really nice and the balcony has a great view which makes it really amazing!
also Mario made the check in and check out really easy for us, and allowed us to leave our luggage there after check out which was really convenient. We will definitely go back there if ever in Porto again :)