While this apartment is not in Lisbon, it is less than 30 minutes away from Lisbon city center (by public bus). And, it is within walking distance to the Belem tower and the Jeronimos monastery. Even that Belen receives a lot of visitors, the apartment is a few blocks away of the crowds which is really good. Public transportation is great, you have a lot of options and if you are lucky you might ride an old style street car. My son loved ridding the old style but most of the time you get the regular more modern type or buses. I would suggest getting a daily pass or tourist card.
There are a few coffee shops nearby, our favorite was Versailles which is a couple of blocks away, the pasteis de nata are amazing. There are also good restaurants nearby, Rui de Pregos is really good.
As said, it is really close to Belem attractions. Please note that the tower and the monastery are close on Mondays. Going to Sintra is quite easy, you could either take a taxi (for about 20 euros one way) or take the train (11 euros one way for our family of four). If you go to Sintra, I would suggest arriving as early as you can, it gets very, very busy.
There are parking spaces very close to the apartment and once we arrived we didn't use our car until we left, as mentioned public transportation is great.
The apartment is in a closed street with other similar apartments.... not all of them are as a well maintained as the apartment we stayed and the street is not as charming as I would have expected but it is a good place. I felt safe and secured at all times. Filipa is a great host, both check-in and check-out were very easy. My only regret is not staying more days in Lisbon/Belem.