The other half of Sigrun’s vault key is in The Oarsmen area in Midgard. In Sigrun’s Curse, you find one key half in The Oarsmen and the other in the Derelict Outpost, then use both to open the Lost Treasury.

Where to look

  • The Oarsmen: advance through the area, then loop back toward the entrance after raising the gate; the other key half is nearby.
  • Derelict Outpost: the second half is deeper in the outpost path and is obtained after progressing through the climb-and-shield sections.

Quick context

The quest is tied to Sigrun’s past and the key halves unlock the Lost Treasury in Midgard. The “family crest” wording seems to be referring to the painted crest and the vault key side quest in this favor.

TL;DR

Go to The Oarsmen for one half, Derelict Outpost for the other, then head to the Lost Treasury to use them.