The Ulla people were a species native to Xirrinda.
The Ulla people enjoyed a considerable amount of music and songs in their life. The legends of the Ulla were taught along with the sound of drums. Singing was used to open the secret doors in the tunnels and deactivate the Rain of Terror. (PROSE: Rain Of Terror)
The Ulla people were once a technologically advanced species. Their technology had overwhelmed them, so they had created the Rain of Terror to rectify the damage they had caused to their home planet of Xirrinda. It reduced them to tribespeople who created thatched houses and kept great paintings to remind them of what they had been and to warn them of the monster they had created.
Their ancestors had also created a machine to deactivate the Rain of Terror. It was hidden deep within a mountain, in a cavern beyond many endless tunnels. The Eleventh Doctor helped reactivate it and the creatures were destroyed instantly. (PROSE: Rain of Terror)