I stayed with Celina and her brother Jesus for six nights and enjoyed every moment.
The apartment is ideally located right at the exit of the subway Moncloa, with lots of bars, restaurants, shops, supermarkets within 5-10 min walking distance, or longer walking distance (30min) from the city centre (Plaza Espana, Puerta del Sol). Ideal to explore the city.
The best about the place, however, are Celina and Jesus - they offer an incredibly warm welcome, lots of good conversations in the kitchen, and they toured me around on the first day until I felt at ease in the district. This is invaluable.
I recommend their place to anyone who is open to new friendships and loves to interact with their hosts. Six stars at least.