Cotter Paluni's World

Cotter Paluni's World was a planet entirely cut off from the universe. Any ship entering the planet's atmosphere was shot down by the red lightning because of "blasphemy". It was discovered by Cotter Palluni, who subsequently died as a result of a crash caused by the red lightning. It is the 26th wonder of the Universe. (AUDIO: Red Skies)

The Tenth Doctor mentioned it as somewhere he wanted to take his companion Donna Noble when he mistakenly thought she was leaving him to stay on Earth. The planet was said to have "lightning skies". (TV: The Sontaran Stratagem)