The flat is very authentic and inside, it's clean. We were pretty surprised to see the constant garbage around the outside of the building. It's important to note that in Europe, the 1st floor is not the ground level floor (which is "0"), it's the next floor up. The stairs up to the flat are extremely steep and there is no handrail. As mentioned in other posts, the neighbors in the apartment above are loud all hours of the night.
PS: We do not recommend using "Welcome Pickups" which Altido recommended several times. They cost 2x an uber and our driver dropped us off blocks from the flat - which we could not find (while having to drag our luggage up and down the hills of Alfama). Once we finally found the flat, we had a heck of time getting into the apartment. Altido sent the housekeeper after over 45 minutes of communicating with them who helped us get into the apartment. There are A LOT of other short-term-rentals in Lisbon and Alfama. We noticed that most of the ones near us had the host actually greeting guest, showing them the amenities, etc. This is not the type of service you receive from Altido.