Lena's place is a great place to base yourself if visiting Berlin. It's very close to the underground and Mitte and East Berlin are a 1 hour leisurely walk away if you like to walk.
The flat is a basement flat, small but is well equipped with everything you need.
Lena is a great host and is very responsive and flexible.
With the flat being a basement flat some noise echoes into the bedroom from the street and surrounding areas in the mornings. This didn't bother us as we were up early anyway.