When you enter the tower, head to the left, take the stairs up, then immediately head to the right. you'll see a set of stairs that go up to a sort of balcony- take those up then look behind you- there are some ventilation panels. If you stand on them you are give the option to "Activate Fan" What is this for?
EDIT: mystery soled. Turns out it was no mystery- I'm just out of the loop Q_Q
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It activates the fan above the Postmasters building. One can have some minimal fun when you stand on it.