Hysperikos Prime
From Tardis Wiki, the free Doctor Who reference
Hysperikos Prime was a planet often visited by the Doctor. It was a place of great learning.
The Doctor was once sent to Hysperikos Prime to warn them of the Skreeth. When he arrived at the planet, the people were either dead or changed into beasts, and the landscape was a waste. (PROSE: The Devil Like a Bear)