Blackshade Isle

To the naked eye, this would seem like just an island in the middle of the ocean, however, this isle is replicated in every Plane of Existence in the exact same location.
Near the center of the equator, this Isle runs to what may be perceived as the center of the earth. Not only that, but it also connects every plane of existence and harbors a series of civilizations with the most powerful of beings stuck in a 'kill or be killed' mentality. Even the few beasts that work together have been known to turn on one-another rather swiftly to gain even the slightest bit of hierarchy. It is believed to be the path Yorpha carved to bring Kierra from inside the planet- unfortunately, the magic that carved this path has only made its inhabitants insane over time, turning them into beasts you'd find nowhere else. Only one person has ever come back from this place, whom of which only went 3 floors down before coming back as the sole survivor.
The Weapons, the food, the armor; Anything and everything you'd find there can be found nowhere else and has tempted many adventurers over the past many years. However, going there would be to tempt death in an entirely new way.

Sole Survivor's notes

"... It was almost as if it could see me no matter what side I came from, it's whole head was nothing but an eyeball! It had tendrils that would come out from underneath its cloak and at the edge of them were these mouths that latched on to all my friends- oh my god it tore them all to bits! I had to get out of there, there was no way we'd beat this thing! I ran, I ran as fast as I could! I went right past every one of those campsites and their damned fountains that gave us false hope and I ran as fast as I could..."