An Isthmus Anchor is an object used to open a portal to another dimension. It must be from one reality, but reside in another. For example, Skulduggery's skull was used to open a portal to the dimension he was in himself. To open up a portal, however, you would also need a Teleporter.

The Grotesquery


The Grotesquery

Main article: The Grotesquery

The Grotesquery is used as an Isthmus Anchor in The Faceless Ones. The Diablerie kidnapped Fletcher and forced him to open up the portal for the Faceless Ones to return. After all the gods were defeated, Skulduggery threw it back into the portal but was then taken in the portal himself. The Grotesquery was no longer an Isthmus Anchor.

Skulduggery Pleasant's skull

Main article: Skulduggery Pleasant's skull

Skulduggery's skull is the second Isthmus Anchor and was used to open up the same portal in Dark Days. Wreath suggested to use the skull in the third book. Valkyrie, with the help of Fletcher and China, used the skull to get Skulduggery back from the Faceless Ones. Afterwards, Skulduggery was reunited with his old skull.