Great little apartment in a great location, we were a group of 4 adults (2 couples) and although 1 of the rooms is bunk beds, it didn't really matter. The price was a lot cheaper than anything else we found.
Things to note:
1. The apartment is on the 4th floor with no lift - not a problem just bare in mind if you have heavy cases.
2. The hosts don't speak English (and we don't speak Spanish) - emails before our stay were translated so asking questions then was simple and they were very quick to reply. We were met at the apartment on arrival and all were shown how to turn the heating/gas/shower etc on and off. There is Wifi so Google translate may help if you have any questions for them if don't speak Spanish!
3. The hot water was slightly limited, worth staggering showers throughout the day and be quick if you're washing your hair!
4. There is a little supermarket about 200m down the road. Out of the front door and right. It's reasonably priced and has most things you need. Branded spirits are quite cheap, no need to buy at the airport (Smirnoff vodka was about 11euros per litre)
5. There is no cooker - sounds silly but once we had been to the shop and stocked up on pizzas we realised there was no oven or grill. There is a hob and a coffee machine. Also a hairdryer and iron.
6. We had an email from the hosts during our stay regarding check-out (which should be 11am). Our flight wasn't until 6pm and they were happy for us to stay there for the day with no extra charge.
7. The location is great, it was about a 30 minute walk to Puerta del Sol, we actually managed to walk everywhere and didn't try the Metro but there are a couple of stops near the apartment if you wanted to.
8. Food - there are a lot of great bars and cafe's everywhere! We had a particularly amazing meal at Miranda's (on the corner of Calle del Leon Street) - not far from the centre. We ate there on New Years Eve, 5 courses and 4 drinks was 54euros (vegetarian also well catered for here)
9. Overall it's a great little apartment, well situated and great hosts. It's a quirky building but was clean and comfortable.