The Genesis Ark was a Time Lord prison ship used during the Last Great Time War to hold millions of Daleks. It was, like a TARDIS, dimensionally transcendental. The Cult of Skaro stole the Genesis Ark and, using a void ship, fled the universe into the Void.
The only way for the Genesis Ark to be activated was to be touched by a time traveller, transferring artron energy to the ark. Incapable of touch, no Dalek could open the ark by any means short of blowing up a sun.
When Mickey Smith touched it by accident in battle, the ark opened, releasing millions of Daleks who proceeded to join the Battle of Canary Wharf against humans and Cybermen.
When the Tenth Doctor returned to the Void all elements that had become saturated in Void stuff, the Genesis Ark would also have been pulled in. Although not seen to enter the Void, it was observed being sucked towards the opening after the Cult of Skaro escaped by temporal shift. (TV: Doomsday)