InNorse mythology,Ámsvartnir (Old Norse "pitch black")[1] is alake containing the islandLyngvi, where the gods bound the wolfFenrir. The lake is only referenced in theProse Edda, bookGylfaginning, written in the 13th century bySnorri Sturluson. In the book, the enthroned figure ofHigh tellsGangleri (kingGylfi in disguise) that the gods and Fenrir fared across Amsvartnir to get to Lyngvi, and there bound Fenrir.[2]
Since Amsvartnir is only mentioned inGylfaginning,Rudolf Simek theorizes that Snorri invented the lake.[3]