At the start I had a day in Frankfurt. I visited the Museum für Moderne Kunst (Museum for Modern Art - http://www.mmk-frankfurt.de/ or http://www.mmk-frankfurt.de/en/home/), which has works by quite a few big names, including Roy Lichtenstein, Joseph Beuys and Nam June Paik. What particularly caught my eye was a large video projection by Carsten Nicolai called unidisplay. For some reason the sound that goes with it has a separate name, uni(psycho)acoustic, though the sound and images are very closely related.
Carsten Nicolai (http://www.carstennicolai.de/) is a distinguished German artist, many of whose works are inspired by geometrical constructions, light and sound.