If you jump on top of the Postmaster’s shack in the Tower, you’ll find yourself standing on a fan, which a buddy of yours can activate by running up the staircase to the right of the shack, getting to the edge of the balcony and pressing the “Activate Fan” prompt. There’s no physical button to press, though: it’s an invisible switch, so just keep an eye out for the prompt to appear. Doing so will cause anyone standing on the fan to be gently blown into the air, though if anyone sees you doing it once, they’ll no doubt want to join in, and you may have a rabble of hardened Guardians taking time out, begging you to catapult them into the air.