Got this question via email, doesn't right a bell with me:
I remember a special issue from the 70s that was a story about Superman still being around thousands of years after all life on earth was extinct, and all life in the universe was extinct also. Superman is bored and spends his days smashing planets to rubble just for something to do. Eventually he battles a giant bug-eyed thing ( I think...). He is visibly old and grey-haired.
Do you remember this issue? If so, what was it?
I'd guess a back-up story in an issue of
Action.