A number of years ago I was on a KLM flight JFK-AMS, it was a weird 747 1/3 passengers and 2/3 cargo. So the upper deck held people as well as an area on the main floor that went back around 10 or so rows behind the staircase that went upstairs. Then there was a wall with a door in the middle. Myself and another passenger needed to use the galley and aske dan FA, he said Ill do 1 better come with me, he open the door and said hows this, we said great. What was behind that wall was the rest of the main floor without any walls , floors, setas , lavs, galleys, etc etc. appx 4 feet on the other side of the wall was a netting that went from side to side and top to bottom, to prevent any loose cargo from slaming into the wall. It was very cold, mostly there were cargo containers that goes on the tracks along with pallets of stuff piled high.
And finally I couldnt believe my eyes there was a horse trailer with Yep a horse in it, along side was this guy sitting next to it to make sure all was well with the horse. The guy was bundled up as if he was outside in a snow storm. The horse was going over to be entered in races, and there were a couple of workers that kept switching off to moniter the horse. This was in the mid 70s.

But boy was I glad when I went back into the heated cabin, man was it cold in there No Heat.