OK. I have been to Madrid many times...but NEVER had the opportunity to stay at the Plaza Mayor! Loved the location. The apartment was clean and spacious, and though I thought it would be noisy, once you close the windows, it is quiet inside! This has an unusual layout, with kitchen and living space upstairs, and then, down a spiral staircase, the 2 bedrooms, which share the full bathroom. I was glad to have the half bathroom upstairs, to avoid going up and down the spiral staircase just to use the bathroom. We stayed mostly upstairs!
Parking is EASY but expensive! Basically, there is a huge public parking garage underground below the Plaza Mayor. I think we paid $75 for 2 days...BUT...worth it if you have to have a car. Once we parked, we never moved it until we were leaving town. Taxis are super easy and cheap...and they now all take credit cards.
There is PLENTY to do around the area. We went on a segway tour and saw a flamenco show. The OLDEST restaurant in the world is just a few blocks away and we had a wonderful experience there. There is an open market just outside the plaza that has amazing food of all kinds.
What made this stay even better was the host (very friendly and responsive) and the price. For the price we paid, it was the most value of any place we stayed in our journey around Spain.