Njagilheim was a planet at the edge of the Last Great Time War. It was mostly water, with only one large landmass. (AUDIO: Nevernor)
Susan brought Rennis here for his exile, following an incident in which he used the Orrovix against the Time Lords. (AUDIO: Assets of War)
Later, a battle in the Time War was fought here, leaving temporal storms in its skies. Leela came to Njagilheim shortly after the battle and met Agata, accidentally creating a time loop in Agata's past. The Orrovix attempted to escape the Time Vortex through this break in time.
Romana II and Narvin followed Leela's biodata trace to Njagilheim and stopped the Orrovix from escaping. (AUDIO: Nevernor)