Bifrost Bridge



The Bifrost Bridge, also known as the magic rainbow bridge which connects all the Nine Realms together, however can only be opened by the guard of the bridge, Heimdall and will only open if permitted;  in fact the bridge is far too powerful for any normal Asgardian, it would even destroy all the Nine Realms if left opened.

Thor
Thor, Loki , Sif and the Warriors Three use the Bifrost Bridge to reach Jotunheim and attack the Frost Giants by surprise after being told by Loki they were going to attack Asgard ; even though Heimdall is not happy letting them cross the bridge. Later, Loki uses Bifrost Bridge again to Jotunheim to ally himself with Laufey, so that they could attack Asgard through another way than through The Bifrost Bridge; by using another passage way.

Once again Sif and the Warriors Three use it to reach Earth to rescue Thor and bring him back to Asgard after being punished to Midgard. In order to prove himself worthy of the throne of Asgard, Loki wants to use Bifrost Bridge to completely destroy Jotunheim, he is able to open it after freezing Heimdall and killing Laufey; during a battle between gods, Thor chooses to destroy The Bifrost Bridge, so preventing the annihilation of the Giants. After the Bifrost Bridge is destroyed it is regenerating itself, and so the portals between worlds are not closed forever. Heimdall continues to guard the Bridge.