Carlos is an amazing host. He is very kind and helpful. Communication was very smooth, though he speaks only Spanish. The place is very well-located and around 25 minutes walking to Atocha. There are plenty of close bus stations (2 - 5 min. walking) to drop you wherever you want. Yet, it is still walkable to the center. The neighbourhood is so safe, well-lit and calm. The room is tiny but very well-organised and has everything I needed. It has a single comfy bed, a nice wardrobe with plenty of hangers, even a TV and most importantly a plug beside the bed ;)
I can't thank enough Carlos for the beautiful stay and I will definitely come back.