There is only one quay at Portimão located on a dusty 1km long plot of land bordering the Rio Arade and situated equidistant between Portimão town (1km) and Praia da Rocha (1km) (Think of a mini Benidorm!) albeit with a lovely beach.
If the vessel is bigger than 40,000 tonnes or have a deep draught, one may end up anchoring off-shore and being transported into the Port by tender as the Arade bar and estuary require dredging to accommodate vessels of greater size.
The Fort of Santa Catarina located at one end of the main street of Praia da Rocha is about 1,5km distant from the main quay. This press article (in Portuguese) about the fort from 2104 reports that it is in a state of degradation: http://bit.ly/1zDRh5L
At present Portimão town becomes more run down by the day, with the local council having the highest municipal debt in the country.
Depending on how much time one has, a tour to Silves, Monchique or elsewhere in the Algarve would be a better choice than a day in downtown Portimão.
Otherwise, basically walk along the riverside into town, enjoy the seafood in some of the river-side restaurants by the old iron road bridge. One place that might be worth a visit en route is the Portimão Museum.
You will see from the photo a vessel moored along the quayside about 500m south of the Museum.
More photos and reports on vessels visiting the town can be seen here on this great site portimaocruises.blogspot.pt