When you first spawn in at the tower if you run to your left and run up the stairs in front of the north side of the tower on that little balcony you will find 5 metal plates on the floor and if you stand over them a activation button pops up and asks you to turn on the fans. What happens if you get 5 people to turn the fans on at once?
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The fan is on top of the postmaster's building. If you activate it it'll lift anyone standing on it into the air.