God of War has always been heavily inspired by mythology. The series' earlier titles drew much of their lore from Greek folktales, but as of 2018's God of War, the series has shifted to a world that's instead rooted in Norse mythology. As a result of this change, Kratos' adventures now take place across the nine realms of Norse cosmology.
Players have already been given a glimpse of six of the realms, although with the exception of Midgard, none of them have been explored in any great detail. With God of War: Ragnarok set in the same world though, it seems likely that future games will take a much deeper dive into the lore of the nine realms as well as the mythical World Tree that binds them together.
10 Yggdrasill
Yggdrasill is a mythical ash tree that connects together the nine realms of Norse mythology. Its branches extend far into the heavens and are home to many creatures including dragons and eagles. It's positioned at the center of the Cosmos and is known by a number of different names. In modern times though, it is often referred to simply as the World Tree.
The World Tree is used as a fast travel mechanic in God of War, with players able to traverse its branches to quickly reach other points within the realm. Harvesting the tree's sap will grant stat boosts while crystalized sap explodes when introduced to electricity. The tree is also used to travel between realms in Tyr's Temple, which exists in each of the nine realms.
9 Alfheim
Alfheim is the home of the Elves. It was once presided over by Freyr, the Vanir God of Fertility and brother to God of War's Freya. It's thought to be a very beautiful realm, although mentions of Alfheim in Norse texts are few and far between. As a result, very little is known about the realm and its history.
This perhaps worked in the developers' favor, as it gave them a lot more creative freedom when designing the realm in God of War. In the game, Light and Dark Elves fight endlessly over control of the Light of Alfheim, with Mimir hinting that despite their light and dark theming, neither side is necessarily good.
8 Asgard
Asgard is the realm of the Aesir and was originally considered part of the realm of men. More modern interpretations place it up in the heavens though. The Aesir Gods were once at war with the Gods of Vanaheim, but the two realms are now at peace. Following the end of the conflict, Odin married the Vanir God, Freya.
It's impossible for Kratos and Atreus to visit the realm of Asgard in God of War, but it's heavily referenced throughout the game. Since Odin locked the pathway to the realm following the breakdown of his marriage to Freya, only Aesir or those invited by Odin are able to enter. It's been prophesized that Asgard will burn when Ragnarok comes, making it incredibly likely that kratos will visit in the upcoming game.
7 Helheim
Helheim was not originally considered to be one of the nine realms, but has been treated as one since the twelfth century. It's a dark and gloomy place where flames are unable to survive and is presided over by the Aesir Goddess of Death, Hel. The souls of those who die from illness or old-age are sent there, but those who die in battle are instead sent to Valhalla.
Kratos visits Helheim several times during the events of God of War. Due to Odin imprisoning the Valkyries, the realm is flooded with souls, many of whom should have been taken to the halls of Valhalla. Hel has yet to make an appearance in the series, although she may well turn up if Kratos returns to the realm in the future.
6 Jötunheim
Jötunheim is the realm of the Giants and is said to be a place of chaos and disorder. It's the birthplace of the Trickster God Loki and was once home to the frost-giants. Although the relationship between the Giants and the Aesir has often been strained, many of the Aesir gods have visited Jötunheim, including both Thor and Odin.
Jötunheim doesn't appear until the very end of God of War, but plays an important part in its narrative's climax. It is here that players learn about Atreus' Jötnar heritage as well as his role in Kratos' fate. It's also the final resting place of Kratos' wife, Laufey, as well as many Giants whose corpses litter the landscape for as far as the eye can see.
5 Midgard
After the Gods created humans, they then created the realm of Midgard to protect them from the Giants. It was made using the corpse of their first creation, the Giant Ymir and is surrounded by a great ocean. It's here that the mighty World Serpent dwells who, according to prophecy, will one day set in motion a chain of events that will lead to the deaths of many of the Aesir and Vanir gods.
Midgard serves as a hub-world of sorts in God of War, with towers for each of the other realms spread out around the Lake of Nine's perimeter. As a result, much of the game's action takes place there. After the conclusion of the game's narrative, the weather in Midgard changes to snow, which is said to be a sign that Ragnarok is near.
4 Muspelheim
Muspelheim is the realm of fire and home to the Fire-Giant, Surtr. When Ragnarok comes, some scholars believe that it is Surtr who will set Asgard ablaze, but this is disputed by others. It's also said that Muspelheim is responsible for the heat in all of the nine realms and that Muspell means 'wreck of the world'.
Although it's possible to visit Muspelheim in God of War, only a small section of the realm is explorable. Aside from an imprisoned Valkyrie, Kratos and Atreus do not meet any of the realm's inhabitants, nor do they see any obvious signs of life. Given that the Fire-Giants will likely play a big part in Ragnarok, it seems probable that Kratos will one day return.
3 Niflheim
Niflheim is a dark and desolate place that is said to be so unforgiving that not even the Frost-Giants could survive there. The mist which covers the realm formed after the waters of Niflheim mixed with the flames of Mustpelheim. Some also believe that it is where the great Giant Ymir first took form.
Niflheim is an optional realm in God of War and can only be visited by reading all of the relevant cipher codes. According to the game's lore, an alchemist Dwarf called Ivaldi was responsible for the realm's mist becoming poisonous. The Dwarf's workshop is the only explorable location in God of War, but it's certainly possible that Kratos will visit other areas of the realm in future games.
2 Svartalfheim
In early Norse mythology, Svartalfheim was the realm of the Dark Elves. When compiling the great Norse sagas, however, the twelfth century mythographer Snorri Sturluson combined the realms of Nidavellir and Svartalfheim in order to make room for the realm of Hel. Despite Svartalfheim translating to 'the land of the Dark Elves', Snorri considered it to be the realm of the Dwarves.
This confusion is somewhat touched upon in God of War. According to Mimir, the Aesir are unable to tell the difference between Dwarves and Elves and so named the realm incorrectly. It's a place that Kratos is yet to visit, with Odin having sealed it off in order to prevent an alliance forming between the Dwarves and the Vanir. Svartalfheim steel does appear in the game though and can be used for crafting some of the game's best armor.
1 Vanaheim
Vanaheim is the realm of the Vanir, the former enemies of the Aesir gods. The Vanir are typically associated with magic and some believe that it is because of this that the two realms went to war. They're also strongly linked with weather and fertility, with many farmers and fishermen praying to the Vanir gods for favorable weather conditions and good harvests.
God of War does not allow players to visit Vanaheim, as Odin locked the pathway following the breakdown of his relationship with Freya. It's possible to see Vanaheim through one of the windows in Freya's house though. The only other person that Kratos meets who has seen the realm is Sindri, who once visited in order to learn more about Vanir magic.