Go Among the Stars

The ending. Cured (Optimal Health) and with the gun disabled at the Enforcement Platform, build the Neptune: launch platform first, then gantry, boosters, fuel reserve and cockpit - a hefty materials bill including ion cubes and a Cyclops Shield Generator, with the blueprints handed out through the endgame story. Climb aboard, run the pre-flight, deploy your time capsule (Leave Only Time Capsules - genuinely don't forget), and launch. Credits, and one of the best endings in survival games.

Historical note: this achievement was glitched at launch in early 2018 and famously refused to pop; it was patched within weeks and unlocks reliably now.