I don't know what the concept is. This is the most cosmic thing in the dungeons, but is it a dungeon, or is it another place? When you get the root chalice, it says that it is another land, but it looks like the dungeons before it.
I can't find any real lore other then what the chalices say.
What is this place's lore
(To clarify, I wish to understand the place itself and mentioned the chalices for their descriptions only, to show what they mention)
Best Answer
Isz Chalices are items that unlock levels within the Isz Chalice Dungeons.
From the item description of the Isz Root Chalice:
This suggests that it is an entirely different location, separate from the "Labyrinth" beneath Yharnam.
After playing the game, I have realised that the whole premise of the game is the world is structured over several planes of existence. "Isz", is one such plane, host to greater beings, and the true depiction of things. The "Land of Isz", technically is always there, just not visible, because your mind is just that closed off to the possibilities that exist within the plane, that you simply can't see them.