Metaphysical engine

A metaphysical engine was a device which allowed travel into the minds or thoughts of individuals, or groups of people, including their beliefs and imaginations.

According to the First Doctor, the TARDIS was a metaphysical engine. As it could travel through all dimensions related to space and time, it was also capable of entering into a person's mind, their imagination. Once, the TARDIS entered the mind of George Smythe, who was trapped in a time loop. (PROSE: Every Day) The Governors had one such metaphysical engine, also called a reliquary. The device they acquired was very old technology, and quite unstable. It could only travel into places believed in by large enough groups of people. (TV: The Metaphysical Engine, or What Quill Did)