I stayed at Javier's house for 1 month. The flat is amazingly located in the very old centre of Madrid.. you'll truly love the location! you'll be able to easily reach all major locations by foot (or public transport if you prefer), and find anything you need!!
The flat is beautifully designed and decorated in all details, amazing colors, lighting and details. It maybe needs a refresh here and there, but overall this a cozy and beautiful place with character.
Be ready to train your legs, as the elevator seems to be permanently out of service and the flat is on the 3rd floor!