Dorit's Seelodge is a piece of beautiful riverlife just 20-30 mins from the hustle and bustle of central Berlin.
We spent 7 nights in the lodge and found it to be absolutely ideal as a place to just enjoy being in the Grunewald and by the Stoßensee river if we wanted peace and quiet, but equally the Pichelsberg S-Bahn is a 10 minute walk away, the trains run every 7 mins and you can get to Charlottensburg, Savignyplatz, Mitte etc etc in no time at all.
We enjoyed a trip to the Autostadt in Wolfsburg, many tours around the historic and modern day sites of Berlin, but some of my longest lasting memories will be just cooking in the Seelodge whilst looking over the river and enjoying watching the boats and wildlife go by.
I'm a big running, swimming, and cycling fan and the surrounding area was perfect for indulging in all 3 - running up Teufelsberg, the only hill in Berlin, was particularly good for training if you're that way inclined.
The lodge is beautiful, functional and incredibly well equipped. If you've got several days to explore Berlin and surroundings, I can't think of anywhere else I'd stay.