The Timeless Halls are the firstfruits of Eru The One's creation. From here he planted the Echelons and holds council with them and receives their worship. Eru is above existence, his presence beyond comprehension, his form uncontainable; thus an miniscule image of The One is present within these Inner Halls, which is the most holy of places apart from Eru himself. Within these walls the Upper Echelons of the entire multiverse gather together. No other beings, including the Implementors are permitted within these walls; their realm of influence ends with the Outer Halls, which encircle the central hub. Here, the Implementors of all universes gather to discuss, share, relate, and do whatever else they do when amassed. Each of these lesser halls is full of passageways that radiate out like spokes of a wheel which link to the Ethreal Planes. These celestial dimenions extend into each of the universes, permitting the Implementors access to the worlds they have been respectively granted authority over.

The only mortal who is known to have entered these halls (and possible the only beings apart from the Implementors and the Echelons) is Zylon the Aged.

SOURCE(S): The Zork Chronicles, A History of Quendor, Zylon the Aged, (Beyond Zork, Zork:Grand Inquisitor)