Grab tickets to watch a game at Helmut-Koernig-Halle. If there's nothing happening while you're in town, you might like to check if there's a tour of the grounds.
This sporting facility is in Innenstadt-West, a place that has loads going for it! Signal Iduna Park, Westfalenhallen, and Westfalenpark Dortmund are other good sightseeing options nearby when you're done at Helmut-Koernig-Halle.