Maybe 30 years ago when I was a kid I got given a book called Supernature by Lyall Watson. Full of amazing things like ESP and cardboard pyramids being able to sharpen razorblades and keep food fresh. Mainly hokum perhaps and it's alleged he copied much of it and made the rest up.
Some time ago I had a plate of cold meat and salad half eaten and nowhere to store until I could finish it off next day. Fridge was too full, I'm a bloke so I don't do clingfilm and the flies would have got to it if I'd just left it on a worktop. In the end, for lack of anywhere better, I shoved it in the microwave oven and closed the door. Next day to my surprise everything was as fresh as when I'd put it in there. A half eaten slice of buttered bread was still soft. A sandwich left on a plate in the lounge will be hard in a hour or two.
I've repeated the procedure many times since. In fact the microwave is now my preferred place to store opened food overnight. It clearly isn't airtight so that isn't the reason. Maybe in some dimension or other all microwave ovens are pyramid shaped. Perhaps a breadbox or a closed cupboard would do just as well but I haven't got the former and haven't tried the latter yet.
Try it sometime. Butter a slice of bread, cut it into three and put each on a plate. Put one in the fridge, one on a worktop and one in the microwave. Leave overnight and see what happens.