We had a great stay at Mariana's flat! The flat is very well positioned, a few minutes away from the train station (where there is a luggage storage facility, in case you arrive early and you don't know what to do with your suitcases). It is also a few minutes away from the Cathedral and the river and is situated in a quiet old street (but it overlooks a garden anyway, meaning quiet nights).
The flat is very clean and has everything you might need for a short and long stay. Communication with Mariana was easy and friendly.
If in Porto again, we will definitely go back to Mariana's flat!