Here's something to think about, but only if you have some interest in heavy metal music.
What is the quintessential metal song?
I realize there are many different kinds of metal music -- death metal, progressive metal, speed and thrash metal, etc. -- but what if a friend of yours came up to you and said, "You know, I have never heard any heavy metal music. What does it sound like? I don't have a lot of time right now, so just give me one song as a starting point and I will explore the genre from there."
What song would you suggest he listen to first?
I'll share my choice later.