I've been to the carnival; I've been to the robber's den.
I've seen judges who are just and unjust.
Can't really judge them; I've been one to make mistakes, too.
I've also seen twins eating a delicious green fruit.
I've sat down in a comfortable rocker,
and eaten a steak pink in the middle.
What a busy fellow I am, yet I don't have a worry.
I've done and seen a lot, and all from a challenge,
But what have I never seen?
Thanks for reading this puzzle! As usual, please include with your answer an explanation for each line of the riddle. (Every line in this puzzle contributes something, by the way).