Our mission — Cross the border into Poland, find somewhere to drink beer and eat pierogi.
Our route — Thanks to Tim for planning this; the official meeting point was Erkner S Bahn station, but a few of us decided to go the extra mile and cycle to Erkner. From there, it was roughly 75km to Słubice, which is just over the bridge from the German city of Frankfurt an der Oder. You can see the route below.
Difficulty — Now, I can only speak for myself here, but I found this to be relatively easy going. If you're comfortable with cycling, then you'll be able to do this route with ease. I did this on a Brompton, and had no issues at all. This was my longest cycle yet, and towards the end I did begin to feel the burn in my legs as the elevation started to increase, on what is otherwise a pretty flat route.
Getting home —From Słubice, you'd need to head back over the bridge to Frankfurt an der Oder (a short 10 minute cycle) where you can catch a train back to Berlin. The trains are quite frequent; at least 1 an hour, and the price is €12.50 for a single ticket — this includes your bike (You don't need to pay for a Brompton, though).
The best bit — Matt's speech after dinner.