I got the writing cube early on Fez, in a room with jump-mushrooms. When I came back, some golden door-like decorations appeared on a wall. Instead of going there, I went elsewhere first; when I came back that reverted to a normal wall.
I've found no way to go through there: did I permanently miss some content, or was it inactive even before, and that was only a decoration?
edit: after wandering randomly in that level, the decoration appeared again, so I guess it wasn't lost content after all.
So, is everything ok and supposed to happen this way at this early stage in the game, right?