If you come by plane, there are a few airports nearby.

Dusseldorf Weeze in Germany is the closest airport (55 – 60 minutes drive). Dusseldorf International is a good alternative (70 minutes drive). You can also fly to Eindhoven or Amsterdam but requires slightly longer traveling (90 minutes to 110 minutes) to Groenlo.
From Weeze or Dusseldorf to Groenlo the most convenient option is to rent a car. From Amsterdam or Eindhoven you can take the train.