You can go by train to Paderborn, with a change at Hannover. For details go to
>> Internat. Guests
According to www.Bahn.de you have to take bus No 460 from Paderborn main station to Wewelsburg. Ask the bus driver where to leave the bus for 'Burg Wewelsburg'. Here's a text in German:
" Guten Tag. Wir möchten die Wewelsburg besichtigen. Könnten Sie uns bitte sagen, wann wir aus dem Bus aussteigen müssen? Danke. "
"Hello, we want to visit the Wewelsburg. Could you please tell us when we have to leave the bus? Thanks."
Forgot to mention there's Paderborn-Lippstadt airport near Wewelsburg, but taking the train is much cheaper.