A cult song by a German cult band, Birth Control. The LP version is 9'49'', but the legendary live version that made it cult, back in 1973, is supposedly as long as 20'58''. Think of this song as a worthy (and equally keyboard-heavy) successor to In-A-Gadda-Da-Vida.
The German True Metal outfit Gamma Ray (a Helloween spinoff) actually named themselves after this song.