Vanaheim (pronounced "VAN-na-hame") is one of the Nine Worlds, more specifically the one inhabited by the Vanir tribe of Norse gods.
After Magnus Chase passes out after healing Halfborn Gunderson, he was summoned to Vanaheim to talk with his father. The fields of Folkvanger, (a small part of the vast expanse of Vanaheim), is where Magnus and Blitz meet Blitz's mother Freya who reigns over Folkvanger. Folkvanger has no natural sunlight because Freya's stunning beauty lights up everything.
The system goes like this: half the honoured dead of the nine worlds go to Valhalla, one of the courts of Odin and became einherjar where they wait for Ragnarok and train for doomsday. The other half of the honoured dead, called the people's army go to Folkvanger in Vanaheim where they too wait for Ragnarok. The only difference is that in Folkvanger and the inhabitants are more laid back. They don't train and when they occasionally do; they quickly get bored of it and don't try hard enough. They just happily wait for Ragnarok and just accept that they're going to die at Ragnarok and the world is going to end. An attitude like that is great to have in life but not so good at Ragnarok where you are fighting for your life. They people's army will charge into battle alongside the einherjar and fight the battle of Ragnarok. Vanaheim is a nice place to be overall and has not much problems. Another important piece of information is that Vanaheim is home to all the Vanir gods such as Freya and Frey. Vanaheim is the Asgard of the Vanir basically. If Magnus hadn't been brought to Valhalla by Samirah al-Abbas Magnus probably would have gone to Folkvanger and became one of the people's army instead of going to Valhalla as an einherjar. He has also given the choice by Odin as well as returning to Midgard. He declines it because he is happy in Valhalla and as an einherjar.