Coming from Frankfurt, take the A5 in the direction of Gießen to the Gambach intersection and then take the A45 in the direction of Dortmund. You leave this at exit 22 Siegen-Süd.
Coming from Cologne, follow the A4 to the Olpe-Süd junction, where you change to the A45 in the direction of Frankfurt. You also leave this at exit 22 Siegen-Süd.
Coming from Dortmund, follow the A45 in the direction of Frankfurt. Analogous to the directions above, leave the A45 at exit 22 Siegen-Süd.