Arnhem's Historische Kelders are a chain of old vaulted cellars below the city centre. They belonged to merchants' houses and warehouses, and walking through them gives a different angle on Arnhem: less Second World War battlefield, more medieval trading town on the Rhine routes.
The cellars are best treated as a short guided or self-guided heritage stop, not a full museum afternoon. They are especially worthwhile on a rainy day or when you want to add a bit of older city history to the usual bridge, park, and fashion-shopping circuit.