On a typically Dutch June day (cool and rainy) I did a pleasant boat trip out of Rotterdam to the mills at Kinderdijk. This is really a classic Dutch landscape - windmills, canals, cow pastures, guys in wooden shoes, and as such is an interesting contrast to the soulless skyscrapers of nearby Rotterdam. It is pretty touristy (they sell brochures in Japanese and Chinese), but it is still a very idyllic place, where you can also watch an interesting birdlife. I'm not sure if its place on the WH list is entirely justified (o.k., there are no other windmills represented), but it is definitely an interesting excursion.