Blood can be donated at Hochtaunuskliniken in Bad Homburg (Ursuler Straße 33) on Wednesday, 20th June 2012 between 3pm and 8pm.
To donate you must be healthy and between 18 and 68 years of age. If you have not donated before, then you must not be over 60. You must take some form of identification with you, such as a passport, that contains a photo.
You can read more about what then happens here (in German).