I submit The Great Deceiver (Live) Box set by King Crimson.

This is a band at its peak. Whetton on bass and vocals and at the time he was one of the best bassists in the world. David Cross on violin. Bruford (formerly of Yes) on drums. Fripp on guitar.

Four disc set. Used to be real hard to get the cd box set but now it can be downloaded. Total improvisation. Serious metal one song, ballad the next, then some free form type fusion jazz the next. Had a rule that if someone started improvising, the rest of the band followed.

Discs 2 and 3 are my favorites.