Master Hibernation Unit

The Master Hibernation Unit was the Cyber-tomb facility located on the planet Telos, a tomb world. (AUDIO: Conversion, Telos) A massive underground complex, it was discovered under the ice and snow of Telos. The tomb held a small army of Telosian Cybermen and the Cyber-Controller in cryogenic suspension, as well as a cyber-conversion unit, a weapons testing facility and a revitalising unit.

The tomb held what was possibly the last of the Cybermen, keeping them alive so the Cyber-race would live on. It was designed to be a trap. If discovered at sometime by humans (which must possess great intelligence in order to solve the Cybermen's symbolic logic control systems), as soon as anybody walked into the tomb, it would seal itself closed, trapping the people inside. The Cybermen would then awake from their sleep and convert the trapped people into Cybermen to continue the species. Afterwards, the new Cyber-race would return to Earth and control it. (TV: The Tomb of the Cybermen)

Other references
Iris Wildthyme claimed to have visited the Cyber-tombs on Telos. (PROSE: The Scarlet Empress)

The Twelfth Doctor referred to the Telos ice tombs when name-checking all of his victories against the Cybermen. (TV: The Doctor Falls)