I Found This Black Mushroom Cave

So i was exploring near the Gert camp and i saw a path going somewhere next to it, there is a cave at these coords: x 149 z -5566, it has some of those black mushrooms in it
I go in the cave and i see (what looks like as a door)
So i try to like find a switch (a pressureplate) which i might have found but it didn't work
So is there someone who thinks this has anything related to ??? or has someone maybe found a way in it ?(if it is a door or not)

 

thers a tier 4 or 3 cant remember in the room in third pic

 

Ye there's a tier IV there the puzzle was removed.

 

ye there is a tier IV chest in that room in the third pic