You could get in contact with Basel Nutters (
http://www.facebook.com/groups/baselnutters/). Many triathletes so running and swimming at the moment, but when the light and temperature is a little more amenable to cycling they do one or two rides each week, often into the Alsace and/or Basel Land.
My favourite was a 90km loop over Passwang. Basel - Aesch - Grellingen - Nunningen - äbi - Neuhüsli - Passwang - Mümliswil-Rämiswil - Langenbruck - Liestal - Basel.
Otherwise just follow your nose, take a GPS to record your route (and maybe get home if you don't see anymore signs back to Basel) and then refine next time