Explain Diglett’s Cave to me.
Well, it’s… a cave. There are Diglett and Dugtrio in it. I think it’s at least implied (or possibly stated somewhere; I don’t remember) that they dug the cave, and it’s not entirely clear why they might have done that. The anime portrays Diglett as being surprisingly organised, and having a long-term plan for managing the landscape in order to maintain and enhance the habitats of other species of Pokémon, so I’m prepared to believe that they could have coordinated on that scale, but I’m lost on why. It could have been part of an agreement with ancient humans, considering that Pokémon other than Diglett don’t seem to use it.