an interior that only appears on forest maps, where the interior will be an abandoned laboratory with several different rooms, for example cells, laboratories, warehouses and containers with creatures that we can release and even a room with a destroyed ceiling showing the sky and leaves of the trees outside.
And my monster recommendation would be a room with a door (the door would "breathe" slowly) where you enter and realize that it has no end and when you turn around you realize that the room has changed to a meat room, closing little by little and crushing you and consequently swallowing you (this monster only appeared for 1 player and for others the door would just be a wall of gooey membrane)