Martin answered my messages really fast, was really helpful, and I had a nice stay in his apartment. It was light, neat and clean, with a comfortable bed, stuff to cook with and clean towels provided. Perfect location: there are two supermarkets (Kaiser and Lidl) on walking distance, a subway station (U-bahn) really close by and just across the street you will find the entrance of club Tresor (don't worry; it's still a quiet place to stay as you will sleep on the other side of the building). I would stay here again for sure!