Thought Elevator

Thought Elevator is a term used by those affiliated with Code-R to designate structures linked with the Geass ability. Bartley Aspirus speculates that some of the Emperor's recent invasions were done to gain control of the devices.

In appearance they are shown as an enormous vertical gateway from which bright light streams. Only two have been shown so far, on Kamine Island and another in the Geass Directorate's city. It is hinted that they were constructed by some long-forgotten ancient civilization.

How It works
The true "way" the thought elevator works remains unknown however it is known that it works through a persons memories or thoughts as explained by Lelouch discovering how they work. such as Lelouch escaping C.C.'s memory zone by the thoughts of wanting to help her. This could point to the Thought Elevator taking a person to worlds or different dimensions based on desires the said person may have (possibly explaining the Sword of Akashas' choose in location)

They apparently serve as an entrance to the Sword of Akasha.