Our group of five had a great time staying at the Costa do Castelo apartment. Francois - who manages the property - was fantastic with communication, always very quick and thorough with his responses. He also helped to organize airport transfers and - on our final day - a van to the train station.
The apartment is located in the centre of Lisbon, just below the Castelo St. George. From here you can walk pretty much anywhere. The view is spectacular, and guests worried about the height should fear not: there is an elevator one block away that will take you down to the main square, and also to a supermarket that is super convenient.
The rooms are very comfortable and quiet. We all agreed that we would recommend this place without reservation.