I think this apartment is a great base for seeing Sintra. It's right in the centre in a beautiful historic building, about a 20minute walk from the train station. There are places to eat and mini markets just outside the door and it's just a couple minutes walk to the national palace and the bus that takes you to all the other attractions. It couldn't be better located and made everything really easy for us.
It's a lovely place inside too: all the bedrooms and bathrooms were comfortable and are really beautifully decorated in a vintage style. The kitchen was very comfortable too and the set-up with microwave, toaster, coffee machine and kettle is ideal for making a quick breakfast before heading out to see the sights.
The booking confirmation we received didn't include the full address (which I only realised a couple of days before we left Lisbon) and we did have difficulty contacting Joana through the AirBnB app so I would suggest trying a text message as I'm not sure how reliable the messages via the AirBnB app are, they maybe don't get through.
Please note there were a couple of cracked window panes when we were there, which Joana said were being repaired but if you are travelling with children it would be a good idea to check that's been done just in case.