From anywhere in Germany to Haus Bommerholz :

1. Go to http://www.bahn.de/international/view/en/index.shtm

2. Type in as destination "Haus Bommerholz, Witten"

3. Another possibility is to be at Witten Hbf at 17:00 on the 21-st of September. There will be a shuttle bus (with a sign TU-Dortmund) waiting to take you to Haus Bommerholz.

If you have any questions, please, contact one of the organizers.