Martas apartment is absolutely worth the money. The location is one minute walk from Puerta del Sol and you are right in the middle of everything and still in a walking distance to most attractions. Of course there are some noise in the late evenings in the weekends, but everything else would be weird since the apartment is so central.
Marta is really easy communicating with and answers quickly when you have questions. We will definitely recommend Marta and her apartment!