The stairway to the heavens.

In Norse mythology Bifröst is the rainbow bridge that connects Asgard, the world of the Aesir tribe of gods, with Midgard, the world of humanity. Bifröst is guarded by the ever-vigilant god Heimdall. During Ragnarok, the giants will breach Heimdall’s defenses and cross the bridge to storm Asgard and slay the gods.