When I can't decide where to go, I may head for a town that takes no longer than an hour to get to by train from Amsterdam -- Utrecht, Haarlem, Den Haag, Alkmaar, Den Bosch, Hilversum, etc. From there I just strike off in whatever direction seems most interesting and ride for as long as I feel like it. Since every town in the Netherlands is surrounded by pretty countryside laced with bicycle paths, all connected by well-signed fietspad routes, this strategy is entirely viable. If I don't feel like paying the €6 fee to put my bike on the train I can just rent an OV-Fiets at the station of each town.
