Folkvanger, also spelled Fólkvangr (Old Norse, "Field of the People") is a meadow, or a field, ruled over by the goddess Freya, and where half of those who die in combat go after death, while the other half goes to Valhalla which is overseen by All-Father Odin.
Freya rules from her palace Sessrumnir which is an upside down ship made of silver and gold.
Magnus Chase and the Gods of Asgard
When Magnus and Blitzen escape Yggdrasil after an attack by Ratatosk, they arrive at Folkvanger. It is so bright at first, that Magnus thinks Blitzen would've turned to stone, being a dark elf. However, Blitzen explains that Freya, his mother, uses her own beauty to illuminate the place. They then proceed to go to Freya's palace.