I stayed in one of the three guests rooms on the third floor of Katrin's house. It's spacious, with fully equipped kitchen and a very clean bathroom, both of which are shared. The house is located in a very quiet neighborhood, with a 10-minute walk distance to the main campus of FU, a postoffice, an U-bahn train station, and a grocery store. It is an excellent choice for those visiting the university.
Katrin is a very nice and warm host. She was extremely patient with my questions about Berlin, and invited me to a few exploration trips to the local area. You also get to meet some other visitors, and for me, this was more than ideal for a travel experience.