Yep, that's meant to be discovered later on in the game. There are no mechanics for discovering subway stations yet, so I think you can take the subway out of the station but you can't make it back.
Viewing post in Train underneath Deep Town Bridge?
Oh alright. So is that why there's so many land borders on the already discoverable places? e.g the nature area just has dirt walls, i think the financial area place has a tile wall and a sign stating the void. Will these land borders be taken away and the destinations just have huge areas between each other that you can tread through to find the subway at the other location? Sorry if that was confusing. Ill try draw what i mean.
Oh yeah, exactly. In the final game I want the player to get to each subway station on foot before they get the ability to travel to it.
Mica in the Sludge Wastes talks about "wild zones," areas outside human settlements. Those will be full of enemies and weird NPCs and fill the space between areas like Deep Town and the Night Market.