The apartment is very close to the train station, which is at 10 min from the center of Lisbon, and 20 min from Sintra (another "must see" in the area). There is no need to rent a car if you do not plan to go really far from Lisbon, as the urban transports are fantastic (trains, buses, uber, ..).
The apartment itself is spacious and calm, and has everything you need nearby (shops, restaurants).
Pedro is a great host, was really quick to answer any question, and gave us great tips on the area.