I'm in mid-marathon-training, so have a 24K, 26K, 28K, 30K behind me, today was a 32K, and in the coming weeks a 34K, 36K, 38K and 40K. I was originally looking for a route to take the S46 to the Endstation Königs Wusterhausen, but it would have been too long for a 32K trying to get around the airport. I settled on a route starting in Blankendfelde which is officially an S-Bahn Endstation although currently with bus Ersatzverkehr to get out there.
Nevertheless I found a 32K route that first went south through a large forest to Rangsdorf, then back up to Glasow which unfortunately including a 3K stretch along a typical Brandenburg tree-alley highway with no bike or running path, so I ran through some farmer's crops, at times very soft running almost like on the beach. Also throughout that area you realize the amount and proximity of planes they have to deal with flying out of BER, definitely something to consider if you ever wanted to live there.
After Glasow it was nice path-running all the way back to the Berlin Wall entering at Lichterade then back out for 1K on the Berlin Wall again, then into a major green area through "Wäldchen am Königsgraben" and then through the full length of Freizeitpark Marienfelde.
By the time I crossed through it, I was at 25K and it was getting dark. The rest of the way home was 80% through green cuts up through Marienfelde and Lankwitz. Unfortunately my head lamp hadn't been loaded but running with my smartphone light worked well enough. Tip: always carry a power bank on long runs, I was loading my phone for the last 5K.
With 2K to go, I messaged into home base for Gisi to start a hot bath for me which I highly recommend after long runs.
The last 5K was tough but much better than last week's 30K. The 2K increase in long runs every week works well.