Lumen (The Light Keepers)

A colossal Lumen, known as the Beacon, was built on a planetoid near Geryon's Eye by the ancestors of the Light Keepers, who were forced to do so by the Lux. Upon its completion, the humans sealed the Lux within, using Lustre to contain it.

With the Lux imprisoned, the Lumen did not move and became green with verdigris. The Light Keepers lived within it and built gantries and conveyors inside of it to transport ore upwards to make hexagonal Lustre panels to keep the Lux contained. Captain Tallis was based in the head chamber, from which he could see through the Lumen's eyes. It was finally activated by the Lux when they learnt of the location of the Light Queen, but, after it damaged the Maldovarium, the Eleventh Doctor defeated the Lux and the Lumen toppled.

The Light Keepers helped repair the Maldovarium and deal with the Lumen's remains, which Dorium Maldovar planned to sell off as "pretty toys". (AUDIO: The Light Keepers)