Gnipahellir (Gnipa cave) is a cave in Norse mythology. Gnipahellir is the home of Garmr, the hellhound who guards the gates of Hel, the Norse realm of the dead. Garmr is often featured chained here until the onset of Ragnarök, at which time his bindings break and he runs free. Reference to Gnipahellir appears in Vǫluspá, Prophecy of the Völva, one of the poems of the Poetic Edda. [1][2]
Now Garm howls loud before Gnipahellir, The fetters will burst and the wolf run free
Völuspá, verse 44