Telos

Telos was a grey and barren planet which was conquered by the Cybermen. Though it was originally inhabitated by the Cryons, they moved underneath the surface when it became too warm, constructing underground cities refrigerated to the zero temperatures the Cryons need to survive. The Cybermen later came to steal the referigerated cities to use for suspended animation, killing most of the Cryons in the process.

At some point in the third millenium a group of archaeologists from Earth arrived on Telos and inadvertently awakened a troop of Cybermen who had been in suspended animation for centuries. Fortunately, the Second Doctor was able to seal them back inside their tomb, at least for a while. Eventually these and other Cybermen awakened and renewed their attacks on Earth and other planets, capturing many Humans and bringing them back to Telos for conversion into Cybermen. The Cybermen used Human whose conversions were unsuccessful as slaves to mine the planet, but they were stopped when their base was blown up.

Though Telos was desolate, but diamonds, vastial and other minerals could be found on the planet. (DW: Attack of the Cybermen)