If you are in Hamburg during summertime (may-september), you should visit the 'Planten Un Blomen' park in the evening!
There are Illuminated fountains
and classical music at one of the lakes. Unfortunately the website is in german and it depends on flash, so that i can't provide the links to the information pdf directly :(
You can get there by clicking the following links on the website:
skip->'Parkanlagen'->'zu den Parkanlagen'->'Planten un Blomen'->'d'
Or visit this english web-page from yahoo:
Concert in the 'Hauptkirche St.Nicolai'.
Unlike other Churches, instead of the classical cross, a painting of 'Jesus with his torturer' hangs from the endless heigh ceiling. I had the chance to attent a Bach concert watching the magical painting. My soul dissolved in the music and lost into the strange, magical, hypnotizing painting... Follow and don't miss a concert at this church. (Located in Klosterstern)