Use the Swamp Key to open Sunken Crypts in the Swamp biome in Valheim. It drops from The Elder, and once you unlock a crypt gate the first time, that gate stays open permanently.

What it’s for

  • Unlocking Sunken Crypts, which are swamp dungeons.
  • Looting iron scraps, chests, and other materials inside.
  • Finding the Bonemass Vegvisir in some crypts, which helps locate the next boss.

How to use it

  1. Go to a Sunken Crypt in the Swamp.
  1. Interact with the iron gate while the key is in your inventory.
  1. Enter and explore; the key is not consumed and can be reused unlimited times.

Handy tip

Bring a pickaxe, because muddy scrap piles block off rooms inside the crypts, and you’ll need to mine through them.

In short: kill The Elder, get the key, and use it to farm Sunken Crypts for iron and progression.