Re: German ID cards
I recollect an incident in Italy, back in (I think) 1994. After a long, hot drive, I had checked in to a hotel on the shores of Lago Maggiore. It being a hot evening, I went down to the lake, and out for a long swim. When I got back, the police were looking for me: apparently I'd been reported as a suspected suicide! They asked for my identity document, and explained that my failure to carry it was technically illegal.
Fortunately they were sufficiently non-jobsworth to accept the sense of not carrying my passport while out for a swim!