Here's a zoomable map of the national bike routes (landelijke fietsroutes) in Belgium and Holland.
No place name labels on this one, so one needs to cross-ref landmarks with a GoogleMaps page.
http://openfietskaart.nl/
Green lines are main routes, blue are a signposted intersection network (knooppunt network).
Short sections of some of these become busy mid-day on the nicest weekends of summer, but only ones near major centers.
The Netherlands is the most densely populated country in Europe, with the highest number of cyclists per capita.
Not one route feels like an Interstate. Ever.