This flat is right at the top of Porto, by the Clerigos tower, which is well known and easy to see from most places in the city. Moreover, it's on the 3rd floor (4th if you are American), so be ready for it if you walk up from the old town or river area. There are 3 or 4 routes up and down to the old town area, either using stairs and little alleyways, or larger streets. Only a 10 or 12 minutes walk. There are tuk-tuks, taxis and trams if walking is not your thing, all close by.
The area is quite lively, Saturday night especially. Luckily the windows are double glazed so it did not bother us. In the street below there are cafes, a convenience store and a pharmacy. Also a fish-ball store. Across the street there is shopping, more cafes and some generic looking food. Also parking and luggage lockers across the street.
We only had one issue in the flat, which the agency fixed immediately the next day. All of our questions were answered within 10 or 20 minutes. The communication was excellent.
Porto is a fun city to explore, and this flat is a great place to stay while exploring.