It is only a 15-minute train ride from Amsterdam to Haarlem with frequent trains. From the station to the windmill is a 15 minute gentle walk.
The city center is compact and everywhere is walkable. There are 4 parking garages ringing the city center.
In addition to your visit to our windmill, you might consider also taking a Hofjestocht (almshouse courtyards tour). Or book a short cruise on the Spaarne with Haarlem Canal Tours or Smidje Canal Cruises Haarlem. Or visit a famous museum such as Teylers, Frans Hals or Corrie ten Boom. Beer lovers should not overlook the Jopenkerk. Various types of Haarlem beer are brewed in this converted church, even gluten free! Try the Adriaan Wit beer!