Oh. I guess I do know what it is then .... ! I helped build part of that thing! I am getting soooo old.
It is a surprise, which is to say "an unexpected or astonishing event, fact, or thing." And it is not my place to say... nor would I if I could.
Pika discovered this in creative! Spoiler: Giant sphere There was some viny, urban stuff right outside and partially outside, so we have reason to believe this is the dome around the mystery.
jack in the box? also, minecraft story mode? that's new (aka I never heard about it or that it was coming out so awesome)