I need a good fantasy apocalypse, any ideas?

I’m working on a homebrew campaign that will have an apocalyptic event occur at some point in its run, the question I’m running into is- what kind of apocalypse will it be?

I already know that, whatever it is, I want it to be the kind of apocalypse where shit is certainly fucked, but not all hope is lost. Given enough time and dedication, the world can eventually adapt, maybe even heal, or, maybe- just maybe. Return to how it used to be.

So, if anybody can toss their hat in the ring with an idea, or your experience with running something like this, I’d love to hear about it. What’s an interesting apocalypse? What’s a good goal after the BBEG succeeded? Tracking him down in hopes of returning life to normalcy? Or was it something that the BBEG didn’t even mean to cause?