The Day After Ragnarok is a cool and unusual post-apocalypse setting.
The background is that at the end of WW2, with total defeat of the Nazi's only days away, the mystic section of the SS (the Ahnenerbe*) summon Jormungandr the World Serpent of Norse myth. Jormungandr is initially hundreds of km long, but just keeps growing until he can literally circle the Earth. Also, parts of him pop into and out of reality at different times. A brave US bomber crew manage to intercept Jormungandr's head, fly straight into his eye, and detonate the world's first atomic bomb. Jormungandr dies but his death throes destroy whole countries.
Roll forward to 1950. Jormungandr's radioactive corpse still circles the world. Well, some parts of it do. Other parts dip back into whatever other reality he was summoned from. The corpse is so big that it extends into the upper atmosphere and changes weather patterns around the world. There's a world map that shows where the corpse's parts are located. In this post-Ragnarok world PCs fight radioactive snake monsters with magi-tech made from mining the serpent's corpse, all set against a cool Cold War vibe.
It's for HERO System, but that's not to say you can't mine it for ideas. Or just play HERO.
* a section of the real SS whose remit had to do with finding (read: making up) evidence to support Nazi pseudo-scientific racial nonsense. Also nicking archaeological artifacts.