Geass Order

The Geass Order, also translated as the Geass Cult or Geass Directorate, is a secretive group that studies and produces Geass users. Its last known location is a large underground city, also called the Geass Order, which is within the Chinese Federation territory. Before the assault instigated by the Black Knights, it was under the control of V.V., and so was presumably under Britannian influence.

Description
Though its location usually changes with each leader, it is currently located in an enormous underground cavern beneath an unspecified desert somewhere in the Chinese Federation. The Geass Order seems to be, for the most part, a fairly modern medium-sized city, complete with streetlights, roadways, ornate buildings, and even an underground train system. The location of the directorate may be the Tengger Desert in our Inner Mongolia, which resembles the desert as seen in Code Geass.

Most of the city is lit with an eerie purple glow that emanates from a Thought Elevator at the head of the city.

Assault on the Geass Order
After the death of Shirley Fenette, an embittered Zero decides to launch an attack on the order as to destroy the existence of Geass as a whole. Crashing through the shallow roof of the cavern, the Black Knights, on Zero's orders, indiscriminately slaughter the city's unarmed inhabitants. While V.V. attempts to stave off the attack with the Siegfried, a group of hooded order members attempt to escape the city with essential Geass research in a bullet train. C.C., however, intervenes and destroys the train before it can exit the compound.

Lelouch, pursuing the wounded (though immortal) V.V. to the Thought Elevator, in which the Emperor can be seen standing. After the Emperor and V.V. exchange a few words, Lelouch finds himself suddenly transported out of the city and onto the Sword of Akasha. Some of the order agents can be seen reporting to Charles zi Britannia after V.V's death implying he's their new leader.

Unnamed Children
When Zero led the Black Knights to destroy the Geass Order, some unnamed children were present who referred to Rolo as "Big Brother Rolo". One of them displayed a Geass power, able to control another person's body. All of the children were killed by Rolo.