At least one of the other random witches in the city is flying! She can see them sitting side-saddle on a broomstick, floating almost leisurely over the city, though far from where she is at that moment. The essence-feeling is muddled from this far away. And the smoke and soot from all the factories and workshops, and the dust of construction, makes it a bit hard to see.
The other collection of witches is a post office. Actually, the post office is just the closest entrance of what looks like a decently sized complex. Storage areas, some kind of training ground, living quarters, offices. Uniformed and armed men stand at the other entrances to the place, carrying - obviously weapons of some kind - a metal tube and a wooden frame and a short blade attached to the end. They look bored. Most of the witches are inside the complex, in the housing buildings or offices. One is walking towards the post office from inside the complex.
The post office itself is inviting and fairly busy. There are lists of prices to carry mail and packages to various places. (Apparently there's also a new tax on mail, according to the signs.) There are orderly queues, scales, carts loaded down with stacks of letters and boxes, busy clerks who occasionally shout 'NEXT!'. There is also a sign that says - 'REFUND NOT AVAILABLE if any witch-carried mail is delayed due to military priority'.