I don't know if that was a story or a running sub-thread, my recollection on this one is very vague. I seem to remember the Antarctic fortress was blown up by his robots or something back when he was trying to become dictator (late Jurgens era, I believe). Then much later, maybe under a different creative tream, Steel helped him build a hyper-sphere which was basically a T.A.R.D.I.S. in that it was bigger on the inside than it was on the outside. So in theory, he could have kept it anywhere - like in his bedroom closet or in his shoe or in the Daily Planet globe or something, which could have been pretty neat - but instead he put it in the Arctic just to throw a bone to us old-timers who had been complaining that the South Pole was the wrong place to have it because it belongs at the North Pole. So there was just this big sphere sitting on a mountain where anyone could see it, which kind of defeats the entire purpose of making a hyper-sphere in the first place. The whole thing just made no sense at all.
I'm pretty sure this is all being ignored in the new continuity, it seems like Supes has a traditional, 3-dimensional Arctic fortress - one that he made himself - with a big metal door again, just like he always has.
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