It is guarded by Heimdall and must be traversed to enter Asgard.  
Hagalaz and Nyd are the first two of eight runes that can be used to symbolize (*) it or its protector.  It was also known as Asabru, because of the many Asynjur who partook in its creation.  On one side of it lay the mythical Urdar fountain, which along with this object will be destroyed by the weight of the Muspell at Ragnorak.  It is guarded by Heimdall and must be traversed to enter Asgard.  FTP, name this famed rainbow bridge of Norse mythology.
Hagalaz and Nyd are the first two of eight runes that can be used to symbolize (*) it or its protector.  
Bifrost or Bilfrost (accept Heimdall before *)