Friedenau - Wannsee - Potsdam - Sacrow - Spandau - zurück

Lovely 70 km asphalt loop starting from Friedenau via:

S-Bahn station Grunewald - Wannsee - Glienicker Bridge - Dutch Quarter - Neu Fahrland - Sacrow - Kladow - Gatow - Spandau/Heestrasse - Jaffeestrasse - and back via Grunewald station.

While you are somewhat 'in traffic' on the outbound leg up to and on the return leg from S-BHF Grunewald, as well as in Potsdam, good bike paths run parallel to the road in parts. Often you can also use the roadway, as this route is heavily frequented by cyclists and motorists are, in my experience, mostly quite considerate.