Key of Dimension

The key!

Description
The key appears to be a wedge shaped implement, with a carved rune of a constellation on the back, and the sigil of the Order of the Dying Star on the other side.

Qualities
As a bonus action, one may use this key to unlock the Chest of the Dying Star. As an action, may put the key into any door or similar object to open a portal to the Sanctum of the Box or to the previous location that the key was used in. This property may only be used once per long rest.

Lore
The constellation is representative of Cerendon, the imperial god of time and magic. The sigil is linked to a priesthood that worshipped Cerendon's relics.