So I’ve seen this door several times with an area behind it and it seems like it can be activated has anyone opened it?
It opens when you are done in the vault. Behind the door is just a fast travel station.
Is there a chest or anything else in there? I’ve never set foot in there since we can fast travel from the map!
It’s part of main quest. Once you have accessed the vault, npc (no spoil) will open that door for you, and there is just a fast travel station behind, nothing else.
You may have skipped the door opening part by fast-travelling from your map.