We have made a very great experience with Mario and his Double Studio. We arrived quite late in the evening but it was not a problem at all. Mario waited for us at the apartment, showed us around and gave us some usefull tips where to go and what to do. The apartment is quite small but for a couple of days completely fine. You have an awesome view from the studio and you are located very central. Everything is in walking distance (central station, super market, river, bus tour, sights. cafes, bars). We even have rented a car and it was not too difficult to find a parking space. Very awesome place for a stay in Porto. You really can enjoy it there.