Okay, this is another idea I hijacked from the Prog Archives forum. Over there it's just obscure prog facts, but I figured here we could extend it to all metal basically. What is obscure? Obviously nothing well-known like: Jordan Rudess played for Dream Theater once in 1994. Maybe something more along the lines of this: Pink Floyd's first album, The Piper at the Gates of Dawn, was recorded at Abbey Road in 1967 – directly adjacent to The Beatles, who were recording Sgt. Pepper’s Lonely Hearts Club Band at the same time.
Okay go!