Thyralabe is an artifact that is unique and exclusive in The Rift region, although some parts of it may be found in any other realms. It makes appearance in several stories that are set in and around The Rift, and later in Eremidia: An Empty Tome.

It serves a purpose as a navigation tool in The Rift, primarily used to locate Great Library and its numerous hidden “shortcuts” to reach the hub of all knowledge in The Rift.

Thyralabe is a construction made from several brass pieces assembled together perfectly, comprising a disc shape roughly in size of an adult human's open palm hand. It resembles an astrolabe in many perspectives, with some exceptions:

• Several tiny, flat gemstones studded on the limb of the instrument, which each of the gemstones can freely move over the groove of the ring;
• The rule's shape is slightly bent sideways;
• The plates used on the instrument projects several spheres instead of one;
• Its rete points out several known “major beacons” instead of stars, each represents known Rift regions; and
• On its alidade, there is a tiny lens on one of its side, in which lens engraved several guidelines visible by the user's eye by taking a peek on the lens from the other side of the ruler.

The name “Thyralabe” comes from the words “θύρα” (“thyra”, lit. door) and “λαμβάνω” (“lamvano”, lit. to take). Literally, the artifact's name means “to take the door”, implying its primary function for reaching the Great Library's entrance doors. Its name came from one of Alexylvan records where the earliest specimen of the artifact was found by Riftwalkers; the date of discovery and date of the record are absent, making this claim a subject of controversy. The record and the specimen are kept in Great Library.

Since its controversial discovery, artifacts of similar feats are then collectively known as “thyralabe”, which then become one of the rare items that can be found in The Rift often sought by anyone with just enough knowledge to use it.

Thyralabe is mainly used as a navigation tool for Riftwalkers when traversing The Rift. Using Lux Primus as the primary guide, one may either pinpoint their position in the Rift or calculate their time spent in the Rift¹⁾.

The plates used in the Thyralabe are commonly known among Riftwalkers as “skyglyph”, and are unique in each major Rift regions due to its relative position upon the Lux Primus.