They were like... 4ft long rectangular prisms, about the circumference of a prickly hug. So bulky but relatively light, just enough to where we even I could lift them over my head for stacking (other people were tossing occasionally, I couldn't manage that). I'm pretty sure I saw a farm machine make a couple, by driving over already cut hay and pooping bales out the back. Each was secured by two loops of red plastic string.
We stacked the rectangles in towers of 3 in the barn, with pallets at the bottom. Each layer alternated in arrangement, kinda like a Jenga tower, for stability. During the loading and unloading we had someone standing several layers up, taking the incoming bales and arranging them properly. We ended up building about about three levels above my head, in the barn!
About half of that back row fell off when the strap came undone, but fortunately we weren't on the road yet. We transferred them to a different trailer and everything worked out.
We only found out about the job the day before, because it depended on weather a lot. Apparently they usually wait for an even hotter day, because the dryer the bales the better (less chance of spontaneous combustion, besides being much lighter). But there was thunder rolling in the distance as we finished up, and sure enough it rained last night. Just in time~
Anyway, the farm also had massive round bales in the barn which had to be moved by rolling into a trailer, two at a time. We didn't have to move many of those though, just fed the horses in the far pastures. There was this big plastic watertank about the same size which we used to fill their water troughs, by holding a piece of PVC up to the outlet. The water pressure made it shoot quite a ways horizontally!
Oh, and I'm sore today, but it's not as bad as I expected. My eyes were crusted shut but they recovered overnight, and the sunburn... isn't nearly as bad as I expected.