A key that unlocks a passage to Nexus
The artifact appears to be a large, jewel-encrusted key though it does not unlock any doors. When it is held by an Eidolon, any movement of the key tears a rent in the air, creating a hole to a realm full of endless stairs and bridges. With a wide enough tear, the key can be used to fashion a doorway to Nexus.
Image from christies.com
The key was discovered in Pontus at the bottom of the sea, where it was retrieved by Sand Veh’kkitor Rah, Guardian of Falling Library on behalf of Librarium Omnibus. Its means of creation are unknown, though it is speculated to have been created in the heyday of Empyrean as “backdoor access” to travel throughout the realms.