What are these brown metal bars with a circular bulge in the middle sticking up out of this fence here?

What is this white plastic thing that folds?

I got it from a career fair stand. You can open it like in the picture or compress it to make it thinner.

Vent-type structure on the front of my house that doesn’t lead anywhere

This was here when I bought my house. There’s a circular hole in the siding underneath but the main wood panel behind it is still there. Is it the remnants of an old vent of some type?

Wood, about half a pound and has a very slightly tacky residue on the back

Several tall poles with spiral "hook" in a park

The poles (about 5-6 of them) were spread around the park, not in any pattern, not along paths and not on any type of playing field. Too tall to reach the hook (at least 3m tall). A friend who lives nearby says he has never seen any plants in pots or similar things hanging from them, since that was my initial guess. Found in this park: https://maps.app.goo.gl/UT3Tp3gG5bRpRuWr8

The farmer has been spreading this rock-like substance on a wheat field after harvest. 1 to 5 inches across. It has the texture of concrete, and a slightly blue tinge.

Gray box with high voltage warning, it is attached to my drain. The silver line goes to the faucet and is neither the hot or cold water, the white rippled hose is the drain from the dish washer.

Big round cylinder on oversized load truck. Google returns only generic "steel tank"

What is this carved wooden panel? Clothes washing apparatus? Part of a chair? Maybe around 100 years old.

What is this tall green plastic box just installed by the city?

So this has something to do with water I believe. They were laying down orange pipe along with them. There are multiple at different spots on the waterline path. They each seem to be right next to the valve that our apartment uses to turn water on and off to the buildings.

What is this handle in the bathroom of my apartment? Fairly old building, no idea what its purpose is