Etienne and Judit's place was a great base for a couple days in Berlin experiencing Christmas markets. It is cozy and very well laid out for such a small space, with a nice view from the bed. Transit connections are quick, despite being a little ways out from the center with cool restaurants and bars a short ride away (or a nice walk were it not winter).
The walk up the stairs was useful for burning off Christmas market calories, but might be a bit challenging for an older traveler. There was a bit of noise from the flat next door as they got out ready in the mornings, but nothing unreasonable.