I recently reread the Time & Time Again storyline from 1991. And boy, does it hold up or what?
The shtick of the story is that Superman gets thrown through various eras in time, he has an adventure in the 1940s, three separate adventures with the Legion (Dan Jurgens is a self-professed Legion junkie from way back), an adventure in prehistoric times, dukes it out with Morgaine le Fay alongside Merlin and The Demon Etrigan in the time of Camelot (6th or 7th century AD) and basically this entire storyline is a ball.
One of the better chapters is Superman's adventure in occupied Warsaw in 1942 in SUPERMAN #54. There he encounters Mr. Z. What's cool about this is that Mr. Z was first introduced in SUPERMAN #51. From Superman's perspective, his first meeting with Mr. Z was #51. But from Mr. Z's perspective, their first meeting was #54. I just adore how they were out of sync with each other like that.
There's something spiritually perfect about Superman having adventures in the Forties. That was obviously important to somebody involved with the creation of this story because two separate issues follow Superman in 1942 America and then 1942 Warsaw.
Anyway. This whole storyline is tons of fun and I recommend it to everyone who considers himself a Superman fan. Read it again for the first time. Because this bad boy HOLDS UP!