Any advice on most scenic driving route from Leiden to Cologne?
It would be a weekday morning in late June.
Well I am planning a similar route and have done several business trips to Netherlands and driven down just south of Frankfurt. I took a route through Eindhoven and Venlo. However a great tip is to use the Michelin Maps and Planner http://www.viamichelin.com
This offers routes both economical and scenic. Worth taking a look.