I was just strolling through this area when i noticed a tower i'd never been inside. Its maybe 6 stories high. It says the elevator isn't functioning and i took the stairs to the 2nd floor where there is a door locked by a terminal. I've looked everywhere and can't find a terminal. Anyone have an idea?

It may be that the door is opened as part of a quest you haven't started yet, and not before. But I'm only guessing.

Sometimes places are one-way. You have to work your way through from somewhere else and when you get to the end of the dungeon that leaves a quick and easy way out. Like the doors chained or barred from the other side. Try finding a way onto the roof, make your way down from there. Or it could be a quest, yeah.

Nope the building is not linked to anything around it, and it's facade is completely enclosed. It's about 6 stories so i'm assuming there are a few floors locked away in there.

And it could be a quest, though i feel i've done every quest i can find so not sure about that.. I may get a picture to help explain it.

You have probably found Ticonderoga, which is a Railroad safe house that opens up during their quests.