The third level, at first glance, looks much like the first two. There are differences, though. The most obvious being that you've hit ground; the staircase, when it existed, went no further. The other is that the markings on the wall have ceased to even resemble language - perhaps there were meaningful marks here, once, but whatever it was tore into the walls again and again until nothing of the original smooth surface remained.
The layer of bones is thicker here than it was on the second floor, and a number of magical items remain intact - though, by your standards, nothing of any great value. Interestingly, none of the items glow; it appears that any weapon that also functioned as a light source has been broken by whatever inhabits this ruin.
Set in the middle of the floor is a large circular stone plug. Once, it would have blocked further progress downwards, but the center of it has been clawed to pieces. Looking through, you can see a long hallway underneath, its sides lined with funerary niches - though the stonework there is in no better condition than what you see around you.