Purchase tickets to see a game at Borussia Park. If there's nothing on while you're in town, you might like to check if there's a guided tour of the facilities.
You'll find this attraction in Rheindahlen-Land. Pay the admission fee and then explore at your leisure. Once you've finished up at Borussia Park, check out nearby sights like Rheydt Castle, Abteiberg Museum and Hindenburgstrasse.