A lovely, spacious apartment located, as Manuela explained, in "the center of the center" in Porto. You are just a few hundred meters from the Sao Bento train/metro and almost all of all of the major attractions are within easy walking distance.
The apartment's layout, with one bedroom in the front and the other in back and two full bathrooms, makes it very comfortable for four people. The large terrace, with its lovely view of the cathedral, is a real asset.
Manuela is an excellent host. She welcomed us with a very thorough orientation to the city, showing us various locations on a map and presenting us with a binder with lots of usual information—including restaurant recommendations. Communication was excellent throughout, and she responded to our one request—for some additional trash bin liners—almost instantaneously.
Mouzinho da Silveira Street is very lively, with lots of activity at all hours. The windows do an excellent job of sealing out noise when closed, but when they are open, you will hear the sounds of passing traffic from the front and people in the courtyard/alley in the back.
Finally, Americans should note that the "the 3rd and last floor" is what we would consider the 4th floor, so be prepared to climb some stairs.