I.M. Foreman programmed the show's course by meditating and communicating telepathically with it. It was a space-time vessel but it had no extra-dimensional connections. It moved through space and time by retroactively building a site and disguising itself before/during/as it moved there. This process took years. It was not designed for instantaneous (or even fast) travel, unlike a TARDIS. Unlike most TARDISes, the show could (and did) travel back into the Dark Time. (PROSE: Interference - Book One, Interference - Book Two)