Arenas are areas on the map where containers with special loot spawn. They are sourrounded by hills so you can’t leave the area easily if a player attacks you. There are 2 arenas on the map. One on the Grunni and one on the Norra island.
Info: This map was posted by the user @esme82 on the Longvinter Discord.
Norra island arena
This shows the arena on the Norra island. It is located at the top of the island.