Panther Cage Key

This is a key, and as such is automatically put into your key ring (a special bag for keys) when you get it.

Source
This is a quest item provided for the quest Hypercapacitor Gizmo (quest), which can be obtained from Wizlo Bearingshiner in Whitereach Post in north-western Thousand Needles.

As a quest objective

 * Hypercapacitor Gizmo (quest)