Is there a darkest side of the moon in Mario Odyssey?

Excuse me, but I'm curious about something I've been hearing about the game Mario Odyssey. Could you possibly shed some light on whether there's a so-called "darkest side of the moon" within the game's universe? I've heard rumors about hidden secrets or areas that might be considered darker or more mysterious than the rest of the game, and I'm wondering if there's any truth to that. If so, could you elaborate on what it might entail and how players might go about uncovering it?