Camping in farmers field in Edale, Derbyshire, many years ago. We'd arrived after dark so didn't see much.
Just got light in morning when i decided I needed the loo.
Hopped over a stone wall and got down to business, just as the 5.30am Manchester to Buxton first train of the day passed on the railway line down in a dip. There's me with my arse to the wind about 20 feet from the window level.
Oh well, at least they wouldn't recognise by face