Our Nagarjuna episode seemed to conclude that ultimate reality is beyond our ability to speak about it. The objects of our experience are a shared fiction, and the most we can do with language is to show that they're fictional; even the terms we use to accomplish this (like emptiness) are themselves constructs, serving only this negative, critical function.
So, is there for Nagarjuna a Kantian thing-in-itself beyond our power to describe? A Tao, perhaps, an underlying God beyond human understanding? "The Void?" Westerhoff says no. Not only are knowable interdependently existing substances incoherent, but unknowable ones are too:
A key element... is denying that it makes any sense to speak of objects lying beyond our conceptual frameworks... These frameworks are all we have, and if we can show that some notion is not to be subsumed under them, we must not conclude that it therefore has some shadowy existence outside of the framework. To this extent our conceptual framework is to be thought of not so much as a map of a country, but as a set of rules for a game. If a traveler brings us news from a city in some far-off land which we cannot find on our map, we conclude... that it must be located somewhere outside of the area covered by our map.
But if somebody told us he had found a new opening gambit in chess but that this could not be written down using the familiar notation, we would be justified in being puzzled. After all, the notation allows us to describe all the... moves of chess... In this case we would conclude not that because of the limited nature of the expressive resources of chess notation this gambit was beyond its grasp, but rather that there was no such gambit. It is not that there are some objects within the grasp of our cognitive capacities as well as some beyond them, but rather that the very concept of an object is something established by these capacities. It is not that parts of the world might not correspond to our linguistic and conceptual frameworks but that the idea of a structure of reality independent of these practices is incoherent.
On this interpretation (and Westerhoff admits that Nagarjuna does not actually state a theory of language; this is an extrapolation from other things that are discussed), Nagarjuna is not like the Taoist saying that anything we can speak of is not the true Tao; he is more thoroughly negative about metaphysics. None of the possibilities for basic metaphysical concepts make sense, and there is no reality beyond our concepts, not even an unknowable, inexpressible thing-in-itself.
This view (which is certainly not universal within Buddhism) rejects the idea of a "Big Self" lurking behind phenomena, an underlying Oneness to creation. It's the view that metaphysics itself is untenable: all there is is the apparent world of samsara, though of course some aspects of this apparent world are easier for us to epistemically access than others, so there are still truths like emptiness and the other revelations of Enlightenment for us to discover, but even the Enlightenment experience does not get us access to reality-in-itself, as there is no such thing.
Why the gross image at the head of this post? Why, it's from The Thing, of course! That's what happens when you do a Google image search for "thing-in-itself."