<< #1:In the old days, Superman had a giant key for the door to his Fortress. It was so big, it was disguised as an directional arrow for high flying aircraft. Is it my imagination, or was there a story in which someone gained entry to the Fortress by crawling through the keyhole?>>
I remember somebody TRYING anyway, and setting off some booby traps. Might have been a depowered Supes himself . . .
<< #2:Now and then Superman would be aided by a crew of Kryptonians who would exit the bottle city and aquire superpowers while maintaining their microscopic size. What was their supposed motivation for returning to the bottle having tasted superpower? Were they given a motive?>>
The were Silver Age friends of Supes, good and pure and true. Also, they didn't wanna be tiny, they'd rather be depowered and normal sized with their friends (although, if I were tiny, I'd rather be all powerful too. Just break the bottle and let the little guys bask in the sunlight)
<< #3:Also bottle city related: There were a few stories in which Superman and Jimmy would descend into the bottle and, for some reason, it was necessary for them to aquire secret identities (a third one for Supes!). I believe they took the names of Kryptonian birds. What were they?>>
Nightwing and Flamebird
<< #4:Was it ever explained why the Kandorans wouldn't be super (albeit microscopic) were they to just leave the bottle? They were Kryptonian after all weren't they?>>
They were! See your question #2. The bottle provided the normal Kryptonian biosphere that kept them unpowered.
Good times, good times . . . .
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