You really can't sneak anything past the Destiny community.
They're finding areas you're not supposed to be able to access, such as The Terminus. Earlier last week, a player found a way in, even though it's currently unfinished and won't be ready until 2015.
Now, another player has found a way to enter another incomplete area, as shown in the video below. It's called The Dark Below, which will be part of the game's first downloadable content expansion. YouTube user Se7ensins shows how he got to the secret area, which should also contain a Strike mission called The Hypogeum. Obviously, he's taking advantage of a bug and now that this is public, Bungie will probably nail it down.
And of course, there isn't much to do in the unfinished area besides wander around. It isn't ready yet, remember? But if you're curious, go ahead and check it out.
Related Game(s): Destiny