We stayed in this apartment hosted by Ana and Mariana and wouldn't hesitate to recommend it. Clean, spacious enough for a few nights, and located in a great spot to explore the castle area from.
The apartment was well stocked with necessities, and equipped with a dehumidifier which we were advised to make good use of (Apparently it gets very humid without one).
We mostly communicated with Mariana and she was very helpful, answering our questions quickly and accurately.
Access to the apartment is up a narrow, steep cobblestone path and would probably not be suited for people with mobility problems. The nearest Metro station is about 15 minutes walk away, however the route is fairly straightforward and gave us no trouble.
All in all we had no problems and would recommend this apartment to anyone interested in exploring Lisbon's old town.