Unfortunately, they had some impromptu building work, so after three out of five nights, we had to move to another hostal. However, they organised it, and we ended up staying in a more expensive room, just around the corner, at no extra cost to ourselves. We would have preferred to have stayed at Fuentesol, because it's such a great hostel, but they dealt with the situation brilliantly.
The location is amazing. The hostel is secure - you have three locked doors, a safe in your room, and 24hr reception, which you have to pass to get to any rooms. The people who run the hostel are so friendly, and even though we can't speak Spanish, and they can't speak English, they were always keen to help. Our room came with more than expected - good shower with hot water all the time, fridge, safe, wardrobe, sink, drawers etc, and a small balcony over looking Puerta del Sol. The atmosphere was amazing, and the shared bathrooms we're clean.