Well, for more precision, the hallways always end like this at some extremity:


And normally they're on the sides of the grounds that actually have things on them. For instance, this is below where Haillenarte Manor is located:


Which means the rest of the hall actually goes under the Last Vigil's platform. If you take a look around, you can see that the hallways seems to be continuing all the way to the other side, under Fortemps Manor.
The real question is though, does that mean there's some way to access it from underneath? I thought maybe the Fortemps Manor or the Haillenarte Manor led there, but I don't think both manors would lead to the same hallway.