Great place to stay, extremely close to Sol (roughly 3 mins walk). The majority of Madrid's sights are all located within a 20 minute walk around the flat (it's pretty much in the middle). Very clean and tidy. Helios was kind and welcoming and also provided some breakfast items, milk and juice which was lovely. The only downside of the flat that I can think of is that it's a little noisy at night but this is to be expected with living so close to the centre of town and it was not a major inconvenience.