
my original theory was they are behind the wall circling the upside down. on the outside of the wall, it looks like that disgusting mess of vines. on the inside of the wall, is vecna’s mind and memories which would look totally different from the upside down itself. if max and holly are in the cave vecna doesn’t want to go into, maybe it’s a memory he can’t bring himself to remember bc it’s too traumatic, therefore that’s why they’re safe there