Bifrost

Yet Asgard is always prey to attacks, so Bifrost is guarded by Heimdall, the most astounding of sentries.

Source: wiktionary

The Younger Edda tells us that Asgard is an island surrounded by ocean that lies west of Europe and which is accessed by means of the rainbow bridge, Bifrost. Hence Asgard, like Atlantis, represents the North American ice sheet. Like Atlantis, Asgard has outlying colonies that lie "along the outer strand of that sea." The Bifrost bridge most likely signifies the ice sheet bridge that spanned Baffin Bay and the North Sea to connect the North American and Greenland ice sheets with the European ice sheet.

Source: wiktionary

The only member of the Æsir not permitted to cross on Bifrost was Thor, the son of Odin and Jordr. Everyone feared Bifrost would bend and break under the weight of the mighty thundergod.

Source: wiktionary

In W. Petrie's book "The Story of the Aurora Borealis” (1963) it reads the following: “One can produce arguments that suggest Bifrost was the aurora."

Source: wiktionary