Portal at Voi

The Cartographer Building is a Forerunner installation in the African Savvanah of Earth, near the city of Voi.

It is the Forerunner artifact revealed in the Halo 3 E3 2006 Trailer. There is a tremendous "storm" building over the desert near Voi, which is investigated by a Covenant Loyalist CCS-class Battlecruiser during the Second Battle of Earth. The UNSC military unit ONI Recon 111, that was assigned to shadow the battlecruiser, reports to Commander Miranda Keyes that the cruiser has "stopped...it's found something". The Covenant Loyalist fleet then makes a full-out assault on the structure, and at least two CCS-class Battlecruisers glass the African savvanah, uncovering the Cartographer Building, not The Ark, as it was originally believed. The Forerunner Dreadnaught lands shortly afterwards and the Prophet of Truth debarks, entering the facility as the Covenant Loyalists place a large vehicular defense force to guard the installation, including a Scarab walker, and large numbers of Brute Choppers and Brute Prowlers. The UNSC attempts to attack the structure, with a Pelican Dropship deploying SPARTAN-117, the Arbiter, and a small force of Marines and Orbital Drop Shock Troopers that land beyond the Covenant garrison as they seek to gain entrance to the Cartographer. Avery J. Johnson leads a second Pelican in reinforcing SPARTAN-117's assault, but is diverted until SPARTAN-117 and his cohorts can clear a northern area clear for Johnson to deploy further reinforcements.

The small strike force works its way up to the Shield Wall, a large impregnable metal wall with a small energy shield. SPARTAN-117 and the Arbiter bypass it, moving down a downhill slope and then entering the Cartographer from the entrance floor. While they work their way up the structure against large numbers of Brute Chieftains, Brute Stalkers, and Jackals, Truth activates the Cartographer, opening a large Slipspace rift above the Cartographer which leads to the true Ark structure, which is revealed to be extragalactic and outside the Milky Way galaxy. Truth and the rest of the Loyalist fleet retreat through the rift as the Seperatist fleet, along with the Arbiter, Miranda Keyes, and SPARTAN-117 pursues them to the Ark, leaving the Cartographer behind.