Wat is "landmark" in Nederlands?
Google gives a number of possible translations, depending on what exactly you mean. Wikipedia links to Oriëntatiepunt (which Google omits).
Personally I would go for herkenningspunt. The words 'historical landmark' don't really have a good direct translation, I would use monument.
mijlpaal: milestone, landmark, mile post, guide mark
baken: beacon, landmark, seamark
bekend punt: landmark
grenspaal: landmark, barrier, pale, guide mark
By the way, you omitted the het in your question: "Wat is 'landmark' in het Nederlands?"
Google gives as a first reply: mijlpaal. That is not the first translation that I would think of. So "Google it" is not the right answer here.
And yet mijlpaal is one of the definitions that www.vandale.nl gives for landmark. A landmark is in essence a feature in the landscape that helps people determine their location, which is the function a mijlpaal has.
Sure it depends a lot on context on what is meant, though the question is what does that translate to.
The first function of a milestone/mijlpaal is to determine the distance along the road.
Mijlpaal doesn't refer to a physical landmark.
You could think of a landmark victory, a defining victory. In that case you can say that victory was a "mijlpaal".