Bifrost

The Bifrost is a burning rainbow bridge that reaches between Midgard and Asgard, the realm of the gods. The bridge ends in Asgard at Himinbjorg, the residence of the god Heimdall, who guards it from the Jotnar. It can be crossed by the gods, but the red band in the rainbow is made from fire that would burn any mortal to ash that might be bold enough to try to cross it.