Something that totally shocked you learning it or realizing it. I might be using the wrong wording here, but ill give you my example:

In Ocarina of Time, we all know the Triforce was cut, or otherwise not something you get in the game, save for in the cutscenes towards the end. BUT - did you know you can actually go find it and see it in the game?

If you have a Gameshark, turn on the levitation code. Go go Zeldas Cortyard in the room where she is, and fly over the wall. When you fall, you’ll land in a pool of invisible water, and underneath the center of the room with the flowers, look down - there it is. Can’t interact with it, but you can see it, and i choose to believe putting it in that exact spot was intentional for lore reasons.

What do you got?