File:Bifröst bridge.jpg

Summary
The Bifröst is the rainbow bridge connecting the Nine Realms, most commonly Asgard, the realm of the Aesir, or the gods associated with the sky and battle (whereas the Vanir of Vanaheim are gods of earth and magic).

It is described as a mystical trail that burns the feet of the ogres, giants, (except Loki and Skadi curiously, as they have made it to Asgard without the Bifröst burning them.) and other races that normally identify as enemies of the Aesir. The creatures that do somehow get past the Bifröst’s burning touch are confronted by Heimdall, the god of surveillance and bridgekeeper. It is said nothing can be hidden from Heimdall; he sees all that happens in the realms, and his hearing is so keen he can hear the grass grow from the ground and the wool growing on sheep.