Rainbow Bridge
Rainbow Bridge is literally that; a bridge in the appearance of a rainbow.
History
Odin was seeing riding up the Rainbow Bridge upon Sleipnir, at the end of "Eye of the Storm".
Real-World Background
The Rainbow Bridge is clearly Bifrost, the bridge from Midgard (the human world) to Asgard (the home of the Aesir) in Norse mythology, which took the form of a rainbow. (The red hues of the rainbow are supposedly fires that run along the bridge to discourage the frost giants from invading Asgard.) At Ragnarok, when Surtur the fire demon and his followers, the Sons of Muspell, ride across Bifrost to assail Asgard, the bridge will break beneath them. (If this has already happened in the "Gargoyles" Universe, the bridge must have been repaired.)