After an initial tight squeeze, Brandon finds that passage opens and the floor seems to level out a bit. The glowing beetle orb, though dim, is sufficient to light the way in the small tunnel. It's more like a long narrow closet than a proper hallway, and Nathros can tell that it's naturally made, a simple crack in the earth caused by something deeper shifting.
The tunnel travels probably few hundred feet, mostly straight east, though only Nathros notices the subtle downward slope over most of it. Brandon leads the way with Sid shepherding the kobold along in the middle and Jeanne and Nathros bringing up the rear.
Brandon notices as the front edge of his orb's light reveals that the tunnel before them opens into a room (about ten feet away).