It's best to rent a car and drive since public transport in the Ardennes can be limiting. Rental cars are available at each airport, and it'll cost around €30 per day. The total time on the road is around 3 hours during this itinerary.
If you have a few more days, it's possible to explore more castles in the area or go hiking in the Ardennes forest. There are many more museums if you're interested, and if you have extra cash to spare, we recommend having dinner at Le Coq au Champs restaurant.
The largest airport near the Ardennes region is Brussels South Charleroi Airport (CRL), located in Charleroi 150km (90miles) away. Another possible airport is Luxembourg Findel Airport (LUX), being 120km (75miles) to the Ardennes. Both airports offer car rentals and public transportation.