The 200

The 200 was a bus that fell through a wormhole and fell onto the Planet of the Dead. The Tritovores thought that the 200 was going to be used to destory them. The bus had 8 passengers and one bus driver when it came through the wormhole. The bus was badly damaged and was stuck in the sand but the Doctor used an alien device to fly them back through the wormhole.

Behind the Scenes
The bus was called the 200 because the episode was the 200th stroyline.