pink floyd’s echoes are long enough. In fact, most of PF's songs are quite long, such as shine on you crazy diamond, wish you were here, high hopes, pulse concert version of comfortably numb, etc. There are also two albums, dark side of the moon and the wall, which can be listened to seamlessly from beginning to end. Hotel California is also relatively long. The melody of every song in pink floyd's The Wall album is basically connected. If viewed as one song...it should be the longest rock song I know.