My wife and I stayed here in mid-October 2019. The location is spectacular - a ten to fifteen minute walk to most destinations. Be warned, Lisbon is called the city of seven hills and walking around Lisbon you sure learn why! This place is just within the pedestrian zone of the castle, so if you want to take an Uber or taxi there, it will drop you off as close as possible, leaving you with a 200–300 foot walk up an incline to the front door.
This flat is up one flight of stairs (no elevator). There’s a window at one end overlooking the square. That room flows into the galley kitchen. The bathroom is across from the kitchen (shower only) and the bedroom, with a door, is opposite the window.
There bed is about 6 inches from the wall on both sides - a tight fit but manageable. The flat got a bit toasty by the evening (our days were in the mid-70s Fahrenheit, evenings low-60s), but we opened the window over the bed and plugged in a fan provided by the host to help keep cool. The bed is a bit hard, but we slept quite soundly after hiking around Lisbon every day. It wasn’t very noisy, but you could hear people in the other flats at times, so if you sleep lightly, bring ear plugs just in case.
The flat manager, Maria, offered to transport us to and from the airport. We agreed to have her pick us up, but the service does cost extra (and likely more than a taxi or uber would have). But, Maria is charming and gave us a brief tour of the city including her favorite viewpoint. She also gave us some nice recommendations for local restaurants and activities.
It is a great place for two, but I don’t think you’d want to squeeze anymore in there.