Starfield: Unlocking the New Atlantis Penthouse by serving the UC Vanguard
While serving the Freestar Collective in Starfield affords players what is arguably the best ship in the game, serving the UC Vanguard through the Terrormorph investigation will eventually grant the player a similarly impressive gift - United Colonies citizenship, and eventually access to the Class One Citizen-exclusive Penthouse Suite; overlooking the entirety of New Atlantis, and offering plenty of room for players to decorate it to their desire. While practically it doesn't offer as much use as a ship, for players looking to fully immerse themselves in the Settled Systems - the Penthouse offers what appears to be the largest and most luxurious housing plots in the game.
Joining the UC Vanguard
Thankfully, joining the UC Vanguard is simple - you'll want to talk to John Tuala in order to join, but you'll already be acquainted with him through the early hours of the game's main story. If somehow you missed him the first time around, you'll be able to find him in the MAST Building in New Atlantis. Once you sign up, you'll have to complete an orientation - you'll be given a brief timeline of the Settled System's history, as told by the United Colonies, and then you'll be tasked with a flight combat test in a simulator. There's 6 waves of enemies, and while you'll gain extra rewards by completing as many waves as you can, you'll only need to pass three in order to be permitted to go on your first mission.
If you want to attempt to clear as many tiers as possible, note that the computer terminal in the flight simulator will offer you temporary buffs you can enable for one tier. If you have a strong enough Security Skill you can unlock the debug option to permanently buff your ship, as well as spawn an ally that will steamroll through enemies. This isn't necessary at all, but you'll get extra credits the better you do - so if you want to go for it, be our guest.
Completing your orientation, Tuala will give you your first mission - a Comms Repair in Tau Ceti. This doesn't go to plan, and instead, you'll be face to face with a Terrormorph threat. Once you return to Tuala he'll offer you the option to start the Crimson Fleet questline; though for the purposes of obtaining the Penthouse, you'll want to continue along with the Terrormorph story.
Becoming a UC Class One Citizen
Through the course of the UC Vanguard's Terrormorph storyline, players will eventually be granted United Colonies citizenship, which offers them the ability to purchase and own land in New Atlantis; near the completion of the UC Vanguard storyline, you'll be granted Class One Citizenship - whose main benefit is the Penthouse suite in question. Much like with the Freestar Rangers questlines, there are many options available to you for how to proceed - we don't know how exactly these choices will impact matters, but by the end of the quest chain we'd imagine it won't matter and any player will have attained Class One Citizenship.
Where to find your new Penthouse
Simply put - once you've obtained your citizenship, stop by the Realty Offices in the MAST District to pick up your keys, and you'll be able to access your new Penthouse through Mercury Tower in the Residental District. Simply take the elevator, and you'll be free to explore and decorate your new home. It's quite the luxurious Penthouse; taking up seemingly the entirety of a floor near the peak of Mercury Tower. Players have multiple bedrooms and bathrooms, a laundry room, a living room, den and office, and more. You'll even have two separate balconies from which to observe the scenic Jemison view!
Now, as we mentioned earlier - the Penthouse is mostly cosmetic, as anything you could do in the Penthouse you could also very easily do in the Constellation Lodge. However, it's hard to deny just how satisfying it is to have earned a view like this; and for players that truly want to make the Settled Systems their home, it would be very hard to deny how fulfilling it is as a reward. If your goal is a place to truly call your own, you can't do much better than this!