Doctor Who: 10 Places The Doctor Has Never Visited On-Screen
5. The Nestene Homeworld
Like the Zygon Homeworld, the home planet of the Nestenes and their Auton soldiers was said to be destroyed in the Time War. So far, it too hasn't appeared on-screen.
Given the name of 'Polymos' in the novelisation of 1971's Terror of the Autons, little is known of this world other than it wasn't too far from Earth - at the edge of our galaxy. Hailing from the planet was the Nestene Consciousness - an intelligent hive-mind race with the ability to control, manipulate, and animate plastic.
First attempting an invasion in 1970's Spearhead from Space, Polymos' Nestene Consciousness arrived on Earth in the form of plastic meteorites. Its attempts to replace world diplomats and officials with plastic duplicates was foiled by a newly-regenerated Third Doctor, and UNIT.
Stored on Earth, one of these Nestene meteorites - really energy spheres controlling the Consciousness - was stolen by the Master. Using it to help assemble a plastic army, the Master gave the Nestenes a second chance at dominating Earth.
It wasn't until the 2005 episode Rose that the Nestene Consciousness said that its home planet had been ravaged by the Time War. Whether its invasions in the 70s were in response to the Time War or if its attempt in 2005 was the first in a new Nestene bid for a planet is unclear.
The Ninth Doctor was willing to help the Nestene Consciousness find a new home that wasn't the Earth. Having already prepped its invasion of Earth, the Doctor and Rose Tyler were forced to destroy it with anti-plastic.