The Outer Worlds

Story mission and can't be missed.

Phineas Playthrough

You get this after finishing the main quest line on Monarch. Return to Phineas and he will give you his navkey to Byzantium on Terra 2. The achievement popped for me as soon as I entered orbit, before I even exited the ship.

Board Playthrough

On the Groundbreaker, talk to Udom and turn in Phineas. Once you finish his quest, he will send you to Byzantium, where the achievement will pop.

The achievement is story related and cannot be missed. It is unlocked when you land on Byzantium. There are two paths through the game—one unlocks the achievement much sooner than the other. The branch decision point occurs on Groundbreaker.

Halcyon Path: This is the shorter route to the achievement. You must talk to Udom Bedford in the Halcyon Embassy. Tell him you know where to find Phineas Welles. Doing so, initiates the main story quest, Balance Due. Accept it and make it the active quest. This is the mission that will reward you by giving access to Byzantium.

Udom says he cannot help you until he gets back his Board Seal. It is currently held by Gladys Culkelly in the Rest-n-Go. Once you acquire the seal and return it to Udom, he will give you the Navkey to Adjudant Akande's Landing Pad. You don’t have to use it immediately. When you are ready, go to your Nav terminal. Select Terra 2 and choose Adjudant Akande's Landing Pad. You will land on Byzantium and pop the achievement.

Phineas Path: This is the longer route to the achievement. When you talk to Udom Bedford, do not divulge any information regarding Phineas or tell him point blank you do not know anything about Phineas’s whereabouts. You must then play through the lengthy main story quest Radio Free Monarch. At its conclusion, go to Phineas’s lab where he instructs you to get a certain chemical and gives you a Navkey to the City Docks on Byzantium. When you are ready to go there, use your Nav terminal and select Terra 2. Choose the City Docks Landing Pad. You will land on Byzantium and pop the achievement.

The achievement is unmissable because, to progress the story, you must obtain the chemical Phineas needs. It is only available on Byzantium. So, regardless of your path through the story, you must eventually go to Byzantium. When you do so, you unlock the achievement.