Alright, /vp/oreans.

What's the absolutely worst place to explore in the entire series?

That one cave/mountain/area that you only dare to go in as many times as the game forces you to; or at most, going there, getting the items and pokémon only found at that place, and never going back?

Mine is easily Mt. Coronet. In fact, I didn't ever fully explore that place, even once. I just rushed in to get the most important items and that was that.