Reading some of the other reviews here, you may be forgiven for thinking you'll be living on the staircase. Let me assure you that this is not the case. True, this being the old part of Alfama, the stairs are steep, narrow and there are 3 flights of them, so if you have a hard time climbing up 3 flights of steep stairs, look elsewhere.
With that out of the way, let's talk about the place itself. The location cannot possibly be any better: very central, right next to the best sunrise/set spots, some key tourist attractions, tram 28 nearby, and plenty of dining options every hour of the day. Oh, and it's quiet at night. The apartment itself is very functional and has everything one needs for a short or lengthy stay in Lisbon. I work remotely, so the desk in the lounge came in really handy. The beds were very comfortable as well. We stayed in February, so it was somewhat damp, but the 2 air conditioners made up for it well.
Overall, a great place to stay and we were very happy.