For Europe, I would recommend the Moselle (Mosel, in German) River. Set up a home base in Trier or one of the smaller towns like Bernkastel or Cochem. You can ride the mostly level riverside bike paths along the river or if you want to challenge yourself a bit more, climb up into the Hunsrück ( to the south) or the Eifel (north). The elevations in either area are not really high but there's lots of steep up and down. The Mosel produces some of the best white wines anywhere, the food is delicious, and the scenery is breathtaking. If you look at the pictures at the link below and think that it can't possibly be that pretty, you will be wrong. Also, you can pick up cycling maps at bike shops or book shops that show all the roads keyed by their suitability for bikes. I don't remember the name of the company but I'm almost certain that they have maps that cover the entire country.
The Mosel Cycle Route