The apartment is very clean and in the absolute best location in Lisbon. Almost everything is within walking distance. If I return to Lisbon this will be the first place I look to stay.
A friend of the owners collected us from the airport and brought us straight to the airport while giving us the guided tour along the way. If this is offered to you definitely accept as it can be a bit tricky to find your way around Lisbon the first day or two.
Attractions that are a must see is the views from Castelo de S. Jorge. Take a trip to Belem also and close to the airport (less than 10 minutes by taxi) is the largest aquarium in Europe. Definitely stop in on the way back to the airport.
There is a fantastic restaurant a few minutes walk from the apartment that has to be experienced to be believed - Meson Andaluz. As a general rule the restaurants are very hit and miss and the interior appearance and price do not reflect the quality of the food. Its definitely worth sticking to lists on Trip Advisor.
Lisbon doesn't do 'traditional' bars generally and it took us a while to find a place to relax and have a drink in a fun environment but we came across a little bar in a side street that is easy to miss but worth a visit to try the local craft beers - Duque Brewpub.
Whatever you do, do not rent a car in Lisbon. Many of the streets are just wide enough for a small car to scrape through and this apartments location will allow you to walk to most of the major attractions.