The Void Ship was an extremely advanced spacecraft designed to traverse the Void, which was the emptiness that existed "between" all parallel universes and all different dimensions. Void ships were considered by the Time Lords, and the Tenth Doctor, to be impossible to build. However, one was created by the four elite Daleks known as the Cult of Skaro during the Last Great Time War. Their featureless bronze sphere the only known example in history of such a vessel. (TV: Doomsday)
When travelling through the Void, the ship was separate from time and space and, until activated, had no detectable mass, heat or radiation, though it could be visible at the specific location where it was chosen to eventually emerge. Due to these properties, people who looked upon it found it deeply unsettling. An invisible barrier prevented anything from approaching the ship, at least while it wasn't active. (TV: Army of Ghosts)
History
During the Time War, four elite Daleks were created (or selected) in secret by the Dalek Empire to constitute a group known as the Cult of Skaro. The Cult was "above and beyond the Emperor himself" and considered merely a legend by the Time Lords. They correctly predicted that the Time War would result in complete disaster for the Empire, and created the Void Ship to avoid the impending destruction. These four Daleks then stole a Time Lord prison ship containing millions of Dalek prisoners (calling it the Genesis Ark), entered the Void Ship with it, and retreated into the Void before the war became time-locked. (TV: Doomsday)
Inside the Void Ship, the four Daleks worked to open the Genesis Ark and free their imprisoned comrades. As they came closer to their goal, the Void Ship began to create spatial disturbances at a location above the ground in Canary Wharf, London, sometime prior to 2007. Perplexed scientists (led by Rajesh Singh) and officials (led by Yvonne Hartman) working for the Torchwood Institute built a skyscraper, Torchwood Tower, to secretly study the disturbance. Eventually the Void Ship became visible, but untouchable.
The Void Ship created a "wake" which connected the universe to an adjacent parallel universe that Tenth Doctor would label "Pete's World". Unknown to the Daleks, their Void Ship's wake created an entry point for an army of Cybermen native to Pete's World. The staff of Torchwood 1 ignored the Doctor's warnings, and unintentionally paved the road for the Cybermen to invade. The same day, the four Cult Daleks emerged from the Void Ship with the Genesis Ark, and were prepared to destroy the Sun to force open the Ark. Before they could do so, Mickey Smith accidentally transferred his artron energy to the Ark by touching it, allowing it to open as the Time Lords' intended. During the subsequent Battle of Canary Wharf, as the freed Daleks began to exterminate the Cybermen, the Doctor and Rose Tyler reversed the rift. The Cybermen, virtually all the Daleks, and presumably the Void Ship itself, were forced back into the Void. (TV: Doomsday)