In Norse mythology, Gjöll (Old Norse meaning "resounding") is one of the eleven rivers traditionally associated with the Élivágar, according to Gylfaginning, originating from the wellspring Hvergelmir in Niflheim, flowing through Ginnungagap, and thence into the worlds of existence. In Hel, Gjöll is the river that flows closest to the gate of the underworld and is spanned by the bridge Gjallarbrú, which was crossed by Hermód during his quest to retrieve Baldr from the land of the dead. It parallels similar mythological rivers from Indo-European cultures like the GreekStyx. The river is said to be freezing cold and have knives flowing through it.
Gjöll is also the name of the rock to which Fenrir the wolf is bound.