Theory

[Sedita]

The door at the diner that leads to mystery box has two steel doors leading to the garage that you can crawl under after you buy the door, perhaps theres another area only accessable by crawling?

Also the obelisk may not be completed, try adding more parts to it, like parts from the turbine and stuff, or see if the obelisk can be constructed in another location.

The billboard and the train and both very suspicious to me keep an eye on them in theater mode when you put turbines down and stuff see if you can find anything strange