I can't imagine a better place to stay while in Berlin. The apartment was immaculately clean, the beds very comfortable, a really good shower with plenty of hot water, nicely furnished, and in the best part of town. The street is lovely and peaceful, but only three minutes away are cafes and hopping restaurants and parks and the subway and anything you may need. There is also a lovely garden behind the apartment house, where you can relax when you have had enough of the streets. Carolin deserves her reputation as super host; everything was easy from check in to check out ( thank you Armin!) she provided little special notions like water and q tips and coffee, was easy to get into contact with, and although we didn't have the pleasure to meet her, we never felt left adrift.
The only sour note was entirely my own fault. I left my rented bicycle unlocked in the hallway, and it got stolen. So heads up for those of you who will rent a bike: never ever leave it unlocked, even behind a locked door.