Mondas is Earth’s twin planet, the surface of Mondas is identical to Earth in every way.
Millions of years ago the Cybermens home planet Mondas drifted out of its original orbit and journeyed into deep space. During this time the Cybermen fitted a propulsion system to Mondas which allowed them to pilot the planet through space back to Earth.
In 1986 the Cybermen reached the Solar System and started transferring the Earths energy back to Mondas. Eventually their planet absorbed to much energy and was destroyed in the process.
Like the Daleks, the Cybermen have a complex and uncharted history. Different Cybermen factions colonised other planets, such as Planet 14 and Telos before Mondas was destroyed allowing the Cybermen race to survive.
Not a lot is known about Planet 14 except that it was colonised before Mondas was destroyed.
Telos is the Cybermens adopted home world, after Mondas was destroyed the surviving Cybermen needed a new planet to rest where its inhabitants would offer little resistance.
Telos was originally homed to the Cryons. The Cryons can’t survive above sub-zero temperatures. They will steam and boil if they are subjected to heat. They lived in huge refrigeration cities, and this is what the Cybermen needed in order to survive.
The entrance to Cyber control
The main control room
A chamber used to revitalise the Cybermen
Weapons testing room
Frozen cyber tombs
Tombs of the Cybermen entrance