Yes, it is a four story walk-up. But unless you have mobility issues, do not let that dissuade you. The view makes all those steps worth it the first time you get inside the door.
The space itself is perfect for a couple. It’s been modernized, so if you are hoping to experience the quirks of an old building you are out of luck. But for us, the modern bathroom and kitchen allowed us to be efficient and got us out enjoying the city quickly.
António was a great host, meeting us at the door when we arrived to give us a tour of the apartment and some (very) local recommendations that you definitely should follow.