Commander Keen 5: The Armageddon Machine

With the Oracle Council safe, Keen flies to the Korath III system and boards the Shikadi's gargantuan Armageddon Machine, a weapon built to detonate the heart of the Milky Way. He must shut down its eight power generators and stop the blast before the galaxy says goodbye.

The Armageddon Machine (Apogee, 15 December 1991) is the registered second half of Goodbye, Galaxy! Built on the Galaxy engine, it raised the series' difficulty and is widely regarded as the finest Commander Keen episode.