Right there are two outside areas, the second one can be accessed by going back to the starting area and exiting through the door at the very bottom where the game starts.
It only opens once you find the ending cutscene. If you make your way to the right you'll eventually run into a room that is full of desks and a fire. After that you'll need to travel up and find the ghosts up there. There's a video walkthrough on my youtube channel just in case. It goes through everything except for the second outside area.