Byzantium is the capital city on Terra 2, and at a certain point you will want to figure out how to get into the city. It requires a bit of effort to get into Byzantium though, but it will be a walk in the park if you follow our guide for getting into Byzantium.
In order to get to Byzantium, you will need to get the "Balance Due" quest. You get this after you get to Groundbreaker and get your Unreliable back in the air. At this point there are a lot of quests to do in the area, and do all of these. When you have cleared the whole city of quests, head to Udom Badford, located in the Halcyon Offices. Talk with him and try to get the bounty quest for killing Phineas Welles. You should not admit to knowing him in the dialogue options. This starts the "Balance Due" quest.
After getting the quest, head to Rest N Go and speak with Gladys. Ask about getting an Official Board Seal, and pay the 8,000 Bits required to get it. When you have purchased the seal, return to Udom Bedford. He will now hand you the Navkey to Byzantium, allowing you to travel there any time you want.
From now on, just Fast Travel to Byzantium, or select the location from aboard the Unreliable. And that's all there is to getting to Byzantium in The Outer Worlds.