The party continues on for maybe a quarter mile or so. The downward slope is gradual, but it does make the walk easy. The tunnel is not completely straight, but it does lead in the same general direction. The air gets a bit warmer as the party walks along. This is the first warm air that the group has encountered down here so far. Up ahead, the tunnel suddenly ends. The tunnel stops in mid-air in the side of a massive cavern. The party has never seen such a large cavern, but they do see a feint red glow in a few places on the maze-like cavern floor below. They also see a few spots of dim light, as if someone has torches on walls. It's as if the party were looking down on one of those shrubbery mazes that nobles have in their gardens, but the maze below is made of stone and a clear view is lost in the dimness of the light.
The group must be in the Cogs. They cannot actually see the furnaces, foundries, and forges below and far away, but they can make a guess at the size of the cavern. It is extremely large and might be close to a half mile in diameter. But distances here are probably deceptive. The floor below might be a few hundred feet down and nothing can be seen in the darkness above. The floor is somewhere below the hundred feet that Tirial, Knoepf, and Artemus can see using the fifty feet of Knoepf's light. Looking at the edges of the tunnel, it's quickly apparent that if there was once a way down, it no longer exists. It is also likely that without a way down, that nobody has come this way in a long time. Getting down will be difficult and fraught with danger, especially for those not skilled in climbing.
But at least the party now knows roughly where they are. It won't be impossible to get out this way, but it won't be easy either. The Cogs stretch under multiple different sections of the city, so the group doesn't know which plateau they are under. But if they go this way, the group would just need to climb down and find a major access tunnel leading out to the surface.