Amazing stay.
Goncalo's apartment is in the most perfect spot possible, it's so close to absolutely everything, yet it's in a very quiet little area. You are literally 2-minute walk, if that, to Rossio Train Station and Rossio Square. 5-minute walk to the Santa Justa Elevador and only ten to fifteen minutes and you are on the waterfront. It also took us just under 20 minutes to walk to the castle. If you haven't worked out by now, I am serious when I say the position is perfect.
Also, the apartment is great. It has a bedroom, separate living, and a separate kitchen, all are big enough for two people to live comfortably. The only negative I had is the bathroom is small and you have to kind of squeeze in to close the door behind you, but I'm really nitpicking here on an otherwise fantastic apartment.
There is a supermarket less than 3 minutes walk away and a pharmacy even closer if you need one. We didn't feel unsafe at all, even when returning to the apartment later in the night. There are loads of restaurants and bars within a stone's throw and there is a very, very comprehensive local guide put together by the host.
As described, there is one flight of stairs to get up to the door, no elevator, so if you can't climb stairs then this apartment is not for you, sorry.
All in all, we had a wonderful stay at this apartment. We would recommend to anyone visiting Lisbon and we will definitely stay here again if we return to Lisbon in the future.