A few people asked about bike rental. I can't vouch for anyone
myself, but friends have told me these folks have a good
reputation:
https://www.facebook.com/RentABike44/
They're over on Mahlower Straße 9:
https://www.google.de/maps/place/Rent+a+Bike+44+in+Berlin+Neuk%C3%B6lln/@52.4797042,13.4201783,17z/data=!3m1!4b1!4m5!3m4!1s0x47a84fbee8c28a6f:0xfa3075bd1b7d33df!8m2!3d52.479701!4d13.422367
Probably the best way to get there is to take the U7 from
Grenzallee up to Hermannplatz, and then the U8 south to
Boddinstraße; the corner of Mahlower Straße is just next to
Boddinstraße U-bahn station.
