Dectus Medallion (Left) is a Key in Elden Ring.
Left half of a split medallion depicting the Erdtree.
Brandishing the medallion with both halves conjoined will activate the Grand Lift of Dectus, connecting the Altus Plateau to Liurnia.
The right half is said to reside in Fort Faroth in the Dragonbarrow, far to the east.
Elden Ring in-game description
Dectus Medallion (Left) Location

Additional Insights Into Dectus Medallion (Left)
- Effect: Join medallions to operate Grand Lift of Dectus
- Rarity: Rare
- Sell Value: 0 Runes
- Dectus Medallion (Left) can be traded.
- On-Hand Capacity: 1
- Storage Capacity: 1