We spent two nights in Porto at one of Marcos' apartments. Marcos gave us easy instructions of how to get in and he made sure we had a cot ready for our baby. We couldn't see him until the last day, but everything was perfect and the apartment was very comfortable and clean. The apartment is in a quiet area with nice views over the river. It's not in the centre, but it is easy to get there by bus, tram or walking (nice 20' walk along the Douro river). We really enjoyed our stay there and definitely recommend it.