A Klingon moon used as a key energy-production facility, whose explosion in 2293 pushes the Klingon Empire toward peace with the Federation.
Praxis is a moon of the Klingon homeworld Qo'noS and the Empire's most important energy-production facility. In 2293, overmining and insufficient safety precautions cause it to explode, as seen at the start of Star Trek VI: The Undiscovered Country.
The USS Excelsior, under Captain Hikaru Sulu, is struck by the resulting shockwave. Spock calculates that the destruction will poison Qo'noS's ozone layer within about fifty years, leaving the Empire unable to sustain its military budget.
Facing collapse, Chancellor Gorkon reaches out to the Federation, beginning the peace process that leads to the Khitomer Accords. The explosion of Praxis is revisited from Tuvok's perspective in the Voyager episode Flashback.