We had a fabulous time at Dimitris's flat. It's a cute 'Hinterhaus' apartment in a typical Berlin residential building, very tastefully furnished and decorated with cool vintage pieces (the kind you find at East Berlin vintage fairs).
The flat is right in the middle of the Kastanienallee hip cafe/bar area, close to lots of cool shops, eateries and places to hang out (also full of hip young tourists, if that's your thing). Mauerpark, Prater beer garden and Kulturbrauerei are all just round the corner.