Had a great stay at Mario's apartment! Very clean, facilities were great and it is perfectly located for walking to a lot of the major tourist attractions - we didn't have to use any public transport during our stay!
As other reviews have mentioned, there are a lot of stairs but it's an attic apartment - what else would you expect! The bed is also a little on the firm side but I suppose that's just our preference!
Would highly recommend for a cute little apartment in a nice part of Madrid.