As someone returning to Hyperborea after a few years away I am curious as to how others use this setting. Do you use it RAW? As an alternate world? Part of another setting? Time travel?
I loved it when I first got 2e, but I already had an established setting I created so I just bolted Hyperborea on as the North Pole, so speak of my setting. As it turned out, I had already conceived of a world with two moons and a limited solar system from whence other beings visited so I just ported that stuff right in. I allow limited interactions between Hyperborea and the rest of my setting, but there are a few gates, most prominently Utrichen Dolmen on the highest plateau of the Mysterious Celestial Empire of Leng, which links to the Plain of Leng in Hyperborea. And through the underworld, of course.
What about you?