Thanks Catymag!
I found someone who created a googlemap and after much trying managed to export it to my garmin.
This is how I did it - someone might find this useful:

goto googlemaps . com
enter "barclays cycle hire" into the search field and click on "show search options"
select "user created maps" in the drop down box and click "search maps"
click the result on the left side
right-Click "View in Google Earth"
copy the URL link into the address field of your browser
replce "output=nr" with "output=kml" and press enter
save the kml file to your computer
goto www . poieditor . com/poi_convert/kml-to-gpx/
convert the kml file to gpx and save it on your Garmin to the \garmin\GPX folder