I have always enjoyed collecting QSL cards. I am a firm supporter of that old addage, “A QSL is the final courtesy of a QSO.”
QSL cards are as much a part of amateur radio as RF!
I’ve recently scanned the cards I have. Some from when I was SWLing – up until about 1970 – and some more recent. Also a collection of those exchanged since I got back on the air in September 2020.