David is a wonderful host and his flat is centrally located. You can walk about 15 minutes in one direction to get to Plaza Mayor or walk 15 minutes in another direction to get to the Prado and Thyssen museums. Add to that the metro stop next to the flat goes directly to Las Ventas bullring and you have Madrid at your fingertips.
The room itself is very comfortable and exterior noise is at a minimum, ensuring you can get a good night's sleep.
David himself is an awesome person and has great recommendations for things to do in Madrid. Highly recommended!