I am a towering structure; I am a tiny footnote. I symbol divinity. I denote death. I could be found in a garden, or a museum, or a citation. What am I?

Every four years Americans go to do this!

I guard the gates to my master's domain, All three of my heads have to share my one name, Dead in, living out is the duty I keep, Unless you have honey cake to put me to sleep

My first word is an age based on metal, an integral part of steel, not simply carbon. My second helps your breathing stay, without them, you would be done. All together, I keep you alive, stuck in a machine, as pressure pulls air inside.

The ones who wrote the most forbidden song in the guitar store. Just leave the led out.