Niflheim (pronounced: NEE-ful-haim) is an optional and unlockable location in God of War (2018) and is one of the Nine Realms of Norse Mythology. Niflheim is known as "The Realm of Fog", due to the cursed mist that plagues the land there.
A major feature of this realm is a vast labyrinth filled with traps and enemies. Located further into the realm is Ivalidi's Workshop, which contains many treasures, some of which can only be obtained using the unique currency of that realm called Mist Echoes. Furthermore, the workshop houses three Realm Tears.
Due to the cursed mist, traversal through most of the realm has a time limit. Once time is up, health gets depleted. Opening chests in the labyrinth will restore some time. All of the chests in the labyrinth contain a number of Mist Echoes. Some of them contain other unique drops, such as Niflheim Alloy.
Sindri is located at the start of the labyrinth, and offers to craft items that will increase resistance to the cursed mist; thus, allowing more time to be spent in the labyrinth.
Deep in the labyrinth is Hildr, who is one of the nine Valkyries.