Telos Minor

So-named by Professor Vansom, Telos Minor was a jungle planetoid located just outside the orbit of Telos, in the Telos system, which the Cybermen used as a factory for mass conversion. It was shielded from detection, meaning scanners could not see Telos Minor at all, and it was not included in any human star maps. This required highly advanced technology for camouflage.

In fact, Professor Parry and Captain Hopper had their whole expedition on Telos, in which they awakened Cybermen from their Cyber-tomb, without knowing there was another planetoid. The Professor had studied Telos for years before gaining funding from the Brotherhood of Logicians. Professor Vansom, on the other hand, had found this outpost, and was busy here adapting Cyber-technology for human military use. (AUDIO: Secrets of Telos)

Flora and fauna
The Fifth Doctor noted that the jungles on Telos Minor included "well-established vegetation", a whole undergrowth, and a thriving insect population, which could mean a whole food chain. By the time he arrived, however, most of the complex life had been converted into Cyber-beasts by Vansom. (AUDIO: Secrets of Telos)

History
On her arrival, Vansom had to crack a code in order to open the Cybermen's base here. She proceeded to experiment with everything she found, converting the local lifeforms into partially Cyber-converted beasts. No one remained alive from her original crew by the time the Fifth Doctor arrived with Professor Parry, Nyssa and Tegan Jovanka.

Vansom also accessed the Cyber-Control database, and used it to learn everything the Cybermen knew about a given subject. This allowed her to access information about the Doctor and his Gallifreyan physiology, as the Cybermen's records were extensive on him. (AUDIO: Secrets of Telos)