Or if pictures aren't good enough for you, I guess you can read my explanation too. The hut at the tower with the postmaster npc has a special function to it that's mostly for fun. However, to take advantage of it, you need at least one other person. One person needs to get on top of the hut and stand atop the turning fan. There are two known ways to do it, both of them being relatively simple. Method number 1 is to climb the stairs next to the postmaster, and then face towards the hut. Dash (Hold in L3 for PS4. I imagine you hold in left thumbstick for Xbox one.) and then jump to the roof. Pretty simple. Method number 2, while a bit more time consuming, nets you the control prompt to mess with people atop the hut. Assuming you've just spawned in, there are two sets of stairs at the left of the hut. One of them will take you to the Tower North section, another will just get you higher in the same area. Naturally, you need to get higher, so take the stairs to the second floor. Guide yourself along the rail until you're at the position closest to the roof of the hut. Jump just beyond the rail to land on the footing just outside it, and then dash+jump onto the hut. If you did method number 2, you'll more than likely have seen a control prompt to "Activate fan." If another player is on the hut, atop the fan in the middle, you can activate this prompt and launch them in midair. Much fun is to be had with this. Go forth, my brethren, and jump atop that silly postmaster's hut!