Most of God of War (2018) takes place in the Norse realm of Midgard.
Midgard is the central realm in the game's explorable world and serves as Kratos and Atreus's home base. The Lake of Nine sits at its center, with a large temple and routes leading to important locations, including the mountain where the pair seek to fulfill Faye's final wish.
The game's magical realm-travel system allows Kratos and Atreus to visit other worlds connected to Yggdrasil, the World Tree. These include Alfheim, Helheim, Muspelheim, and Niflheim. Midgard remains the main hub, even though major story events occur beyond it.
Asgard and Jötunheim are especially easy to confuse with Midgard. Asgard is associated with the Aesir gods, while Jötunheim is the realm of the giants. In God of War (2018), Jötunheim is the destination of the protagonists' journey, but Midgard contains most of the game's exploration and early story.