Cache of the Legion

The Cache of the Legion is a "chest" found in The Mechanar, one of the 4 instances in Tempest Keep. It is located next to the elevator that leads to the second floor. It is locked and unpickable so you must use the Cache of the Legion Key to open it. The key can be created by combining the Jagged Red Crystal and Jagged Blue Crystal which are looted from Gatewatcher Gyro-Kill and Gatewatcher Iron-Hand.