Voi is located about 140 kilometers away from the coastal city of New Mombasa, and on the edge of the Tsavo National Park, the largest wildlife reserve in the region. The town served as the crossroads for railway lines between three Kenyan cities, including Mombasa and Nairobi. A highway known as A23 or Tsavo Highway also runs through the town. By the 26th century, Voi is a futuristic worker town, and it is filled with mechanical factories and shoreline buildings. Multiple water pump houses managed by the GWC Trans-African Pipelines, such as the Voi Municipal Water Pump House 03 around 17 kilometers from Voi, take care of the water supply in Voi.
In the mid 26th century, Voi is situated beside a large man-made ocean inlet, leading all the way to New Mombasa on the coast. As a result of the increasing amount of industry in Voi, it was decided to construct a waterway to carry cargo from the facilities in Voi to the Orbital Elevator in New Mombasa and other locations around the globe. The shorelines of the inlet are full of warehouses and docking structures. A ferry service was also constructed to carry cargo and people along the canal. Along with that, the Voi River still runs through, providing easy transport up and down the river for the industry. One of the most prominent industrial facilities in Voi was the Factory Complex 09 of the Traxus Heavy Industries, located on the shoreline.
About 100,000 years ago, when the Forerunners discovered Earth near the end of the Forerunner-Flood War, The Librarian landed on Earth near Voi. There, she oversaw the creation and subsequent burying of the Ark Portal structure, which would be hidden for thousands of years to come.
Voi has a long history. The town is centuries old, and was formerly a simple market town. According to local history the name of town comes from a slave trader called Chief Kivoi who settled near the Voi river around the 17th century. There after the town grew as a trade post between the local Taita people, other Kenyan tribes and Arabs. The town started to grow at the end of the 19th century when the Kenya-Uganda railway was constructed. People started to move in to work on the railway and the nearby Sisal estates.
Over the many years, Voi evolved into an industrial city and an industrial port.
- Main article: Battle of Voi
When the Covenant Empire invaded Earth in 2552, the general region between Voi and Mombasa became their top priority due to the Portal buried underneath it. When the New Mombasa Orbital Elevator collapsed on October 20, 2552, debris rained down upon Voi and the surrounding region. During the following weeks, the Covenant Loyalists occupied the city and placed heavy defenses around their excavation.
On November 17, due to the return of John-117, the UNSC was ready for a counterattack. By disabling a Covenant Anti-Aircraft Battery from the ground, the UNSC would be able to assault the Prophet of Truth's Forerunner Dreadnought resting on the center of the Portal.
The Master Chief arrived in Voi via the Tsavo Highway and joined up with the Arbiter and a large group of Marines. The battle for the city begun with the UNSC attacking entrenched Covenant Loyalist forces. Together they destroyed multiple Anti-Air Wraiths, a Scarab, and the Covenant anti-air gun. With the anti-air forces destroyed, Fleet Admiral Terrence Hood's ships attacked the Prophet of Truth's Dreadnought, until Truth activated the Portal to the Ark and escaped through it, with his fleet following.
After this, a Flood-controlled ship slipped in, and crashed in at the western edge of the city. This ship was full of Flood, and the Master Chief and the Arbiter began to fight this new threat. Under orders from Lieutenant Commander Miranda Keyes, they started to move to the downed Cruiser, hoping to destroy it and contain the Flood. As they neared the Cruiser, the Covenant Separatist fleet arrived, led by Shipmaster Rtas 'Vadum. The Separatist flagship, Shadow of Intent, deployed Sangheili ground forces to assist the Humans.
The Humans learned that the Separatists were looking for the AI construct Cortana, who was supposedly aboard the Flood Cruiser. Separating from the Arbiter, the Chief went aboard the Cruiser. What he found was not Cortana, but a damaged message left by her. As he was inspecting it, 343 Guilty Spark arrived to repair Cortana. All Human and Elite forces retreated to the Shadow of Intent as the fleet glassed Voi, therefore destroying all Flood in the vicinity and preventing the parasite from spreading any further.
Voi was terminated as a result of the excavation event, only a few industrial buildings remained, which were promptly demolished by Separatist activity at the end of the Battle of Voi.
Voi is a key location in Halo 3. Three successive Halo 3 campaign levels - Tsavo Highway, The Storm and Floodgate, take place in or around Voi. The multiplayer maps Foundry and Ghost Town are also set in or in vicinity of Voi. More specifically:
- Tsavo Highway, the third campaign level, takes place along the Tsavo Highway, leading to Voi.
- The Storm deals mainly with the character assaulting Covenant forces entrenched in Voi.
- Floodgate deals with clearing the Flood from the city, although the city is eventually glassed by Covenant Separatists.
- The town of Voi was actually first seen in the Halo 3 Announcement Trailer more recently to the launch of the game. The only part seen was the billboard on fire (Floodgate) and the Master Chief emerging from the destroyed elevator out of Crow's Nest which wasn't near Voi at all.
- There is a SAM launcher similar to the one on High Ground pointed directly at the AA battery.
- It appears that the factories in Voi may have been used to stash firearms during the battle of Voi.
- The last movement of the Halo 2 Soundtrack is called "The Road to Voi".
- One of the ferries used to transport cargo across the ocean inlet is encountered stranded on a beach during the level The Storm.
- This is probably due to the fact that the area around Voi was drained of water during the Covenant's excavation of the portal.