The Rainbow Bridge was the crystalline, prismatic bridge that ran from the palace at the center of Asgard to Heimdall's Observatory at the edge of Asgard. The Rainbow Bridge harnessed the dimensional energy of the Bifrost and channeled it into the observatory, allowing the Asgardians to travel instantaneously within the Nine Realms.
Thor and his companions traveled across it on horses on their way to Heimdall and to Jotunheim. On Thor's return to Asgard, he and Loki battled at the entrance to Heimdall's Observatory which resulted in Thor shattering the Rainbow Bridge and destroying the energy output of the Bifrost, preventing Asgard from being able to freely travel within the Nine Realms; this resulted in the outbreak of raids throughout those realms.
After the Chitauri Invasion, Thor and Loki transported themselves back to Asgard using the Tesseract. Heimdall used the Tesseract's power to repair the Rainbow Bridge, allowing Asgard to harness the Bifrost once more, and transported the armies of Asgard across space to quell the uprisings.
During the Second Dark Elf Conflict, Heimdall noticed the Dark Elf ships approaching Asgard so he ran up the bridge's suspension to attack the ship and deactivate the cloaking mechanism. After he successfully destroyed the ship, several more ships uncloak and invade Asgard. Heimdall activates a force field around the palace, transferring a signal through the Rainbow Bridge.
- Not to be confused with the Bifrost, the Rainbow Bridge was the physical bridge in Asgard linked to Heimdall's Observatory while the Bifrost is the energy bridge that physically transports you from one planet to another. In Thor, the Bifrost is also referred to as a "rainbow bridge"; this is due to the Bifrost's prismatic energy resembling the colors of a rainbow.