My Absolute Favourite is The Neue Wache (the New Guardhouse) on Unter den Linden in Berlin. The simplicity of the room and the silence struck me. Neue Wache has become the "Central Memorial of the Federal Republic of Germany to the Victims of War and Tyranny". More information: http://www.berlin-tourist-information.de/cgi-bin/sehenswertes.pl?id=13352&sprache=english