I found that the gatehouse in Blackreach seems to be a dead end, unless I am really stupid. Would this be a possible DLC portal location?

I guess I have to ask what you mean by Gatehouse? You mean the Great Lifts?

There are three Great Lifts in Blackreach. Each of them has a sort of "pedestal", not sure if that's the right word, but anyhow, a stone sort of obelisk thing, a few meters in front of the gate. There's a button on the obelisk, which if you push it, will activate and unlock the Lift.

If that's not what you're talking about, I'm apparently confused about what you are asking?

Its possible that this area is opened from the top.

I think I know what he means. There is an area called the [Something] Gatehouse, one of the structures. But when you go inside there is a room and blank wall. It doesn't go anywhere. I'm not sure if there is more to it than that.

The blank wall is in the Raldbathr Deep Market, if you enter it from the Blackreach side. It's one of the access points that lead into Blackreach. You have to open it from above though.

Then there is Mzinchaleft Gatehouse, which is also a Blackreach access point. You need the attunement sphere in both places.

<sup>Is it this?

http://www.uesp.net/wiki/Skyrim:Raldbthar_Deep_Market</sup>

Ah, I think I found it: http://elderscrolls.wikia.com/wiki/Mzinchaleft_Gatehouse

Yes, if you walk out of the elevator that takes you to the surface, and go up a hill through a door, there is a blank wall. The building is named as some kind of gatehouse. If you look closely at the ceilng and floor, it looks like there may be a lift or maybe a hidden door. There are no levers or switches in this room. It looks like pretty much a dead end. That is why I think it might be where a DLC may start. The elevator to the surface is something different. Anyone know if there a second lift that takes you to inside of the dwemer ruins?

Can you be a bit more specific? There are many elevators in Blackreach.

you know....the one with the doodad next to the thingamajig.

@OP....more than likely it's just an un-finished dungeon/zone they didn't get to put in before release date. no way to know for sure. in any case, sounds like a good place to mod something in.

Oh cool, let me google that... *rolls eyes AND sighs* LOL =p

Those are opened from the dungeon above using the Attunement Sphere given to you as part of http://www.uesp.net/wiki/Skyrim:Discerning_the_Transmundane. When used above, a spiral staircase opens taking you down to the upper level of the shaft.

I only know about two elevators in Blackreach. One is at the end where you find the Elder Scroll. The other elevator is not far from where I killed the only giant I found there. If you go to the right when facing Sinderion's Place and past a tower, you will come to the elevator. This is the one that goes to the surface. If you walk out of the elevator and keep going up a hill, you come to a building with one door that says M@*@%*$% Gatehouse, (can't remember the Dweemer name). Behind the door is a dead end. The far wall is not flat and has grooves going verically. This is the mystery.

THAT IS Mzinchaleft's Gatehouse! You access it from the top with your attunement sphere. Mzinchaleft is the ruin where you find Mjoll's sword Grimserver. In the last room where the sword is, you will find the gatehouse. You then use your attunement sphere on the contraption, it will open up, you take the stairs down to Blackreach. It's not a mystery. LOL

That place is not in Blackreach. It is where you first find your way into Blackreach.

Thank you. I was a mystery to me. So there are two entrances to Blackreach from Mzinchaleft. One is outside and the other is inside the ruins.

Most Dwemer ruins that connect to Blackreach have a way into it via the ruin, and then also a great lift.
You cant go from Blackreach to a ruin if you havent opened the stairs yet in the ruin and you cant get from a lift into Blackreach unless you have opened the lift first by going up from within Blackreach.

Exactly. In most cases, you have to access Blackreach through a Dwemer ruin with the Atunement Sphere. Once you are IN Blackreach, you can then activate the great elevators that take you back to the surface.