Afterspark

The Afterspark is a wasteworld of an afterlife, where lost lives, spent sparks, and things that once were go.

Fiction

IDW Generation 1 comics

After awakening from his "sacrifice" to cleanse Vector Sigma of the D-Void, Optimus Prime thought he was in the Afterspark. Subsequent exploration revealed his belief to be incorrect; the world was Cybertron itself in a period of rebirth. The Death of Optimus Prime

Primus: You, Me, and Other Revelations