This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Norse Mythology
Ragarök is really the Nightmare Fuel-version of Hilarious in Hindsight. First considering Hati: a wolf big enough to eat the moon. He must be larger than the earth and have his own gravity field. Then consider the enviromental effects of the moon being eaten. Then Jörmungadr, he encircles the whole god damned earth! His head must be larger than Great Brittan! It said that when he writhes it causes tidal waves. Condiering his size those are freaking 2012 sized waves. Then Fenrir. He eats the freaking SUN! How larger is he really? Considering the sun is more than a hundred times bigger than earth, Fenrir is even bigger. And Níđhöggr is still supposed to be larger than Fenrir. And when Fenrir eats the sun, half of the world would see him do it, then 8 minutes later the sky would go black forever and the Earth would likely be thrown out into deep space along with the rest of the solar system unless it would all be drgged into Fenrir. Fimbulwinter indeed. Granted, the Norsemen knew little about gravity or how big the sun and the moon really was, but this is not the point of this trope is it?
Náströnd (The Bay of Corpses). Dear gods, Náströnd! This is where Níđhöggr lives and the evil doers are sent according to the Norse myths. From the roof of the hall hangs serpents who drops venom and there are rivers running with venom, it's cold and there is no light. And Níđhöggr sucks corpses. This is where the most evil people are sent, wolfish murderers (killers of the defensless), the ones who seduces another’s close-trusted wife and those who gives false oaths and perjure.
The binding of Loki.
The Valkyries. Read Darrađarljóđ (The Song of Darts). Just read Darrađarljóđ and you get the point.
The warp is made of human entrails; Human heads are used as heddle-weights; The heddle rods are blood-wet spears; The shafts are iron-bound and arrows are the shuttles. With swords we will weave this web of battle.