Cycling highlights include the quality bicycle infrastructure in Muenster:
More than 200 long-distance cycle routes in Germany offer opportunity for sightseeing in cities and for romantic rides through natural landscapes:
http://www.germany.travel/en/leisure-and-recreation/cycling/cycling.html
The German Cycle Network:
http://www.radnetz-deutschland.de/en.html
Advisory cycle lanes outside built-up areas:
http://www.nationaler-radverkehrsplan.de/praxisbeispiele/ (also includes international examples)
Stadtradeln (cycling challenge for a better urban climate): http://stadtradeln.de/ (German language only)
Bike to Work (companies challenges, etc.): http://www.mit-dem-rad-zur-arbeit.de/bundesweit/index.php (German language only)