I've spent the last 2 winters sorting out large areas of my plot that have been covered and have dug out all sorts of stuff. The most impressive things have been the massive slabs of concrete!! They were too shallow to ignore, so had to come out. Each one must have taken at least 3 or 4 hours to dig out and shift off the plot!
Blimey! I haven't dug anything as impressive as that, but I keep finding the paper pull-tops from plastic milk bottles. After 4 years I am still finding them! 😀