We came to Madrid for 4 days as a couple and we loved staying in Sylvia's flat! It's really pretty, cosy and clean. The organization was simple and Palany welcomed us, quickly and in a friendly way. The apartment is in a nice neighborhood, close to malaseña and chueca. Another good point, Sylvia allowed us to keep the keys and leave our luggage until 6pm.
The only problem we had was that considering it's in a basement, it's really keeping a fresh temperature so we got a bit cold during nights (but there is a heater if necessary and it must be really nice in summer!). We definitely recommend this apartment.