A Void Ship was a spacecraft designed to explore the Void that existed between dimensions. It appeared as a golden sphere until it was activated, at which point it opened up to reveal the occupants. There was no evidence that the ship could actually touch its surroundings.
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 was visible. An invisible barrier prevented anything from touching the ship.
It was thought to be impossible, but it did exist. The only known Void Ship was used by the Daleks of the Cult of Skaro to escape the Time War with the Genesis Ark. It is unknown if they built it themselves or if it was constructed for them. (TV: Army of Ghosts / Doomsday)