Nagarjuna was the first Buddhist philosopher to elaborate the doctrine of the Two Truths, which has since been interpreted in different ways by different figures. In the Mulamadhyamakakarika, the Master writes:

"The Buddha's teaching of the Dharma is based on Two Truths: a worldly truth of convention, and ultimate truth. Those who do not understand the difference between these Two Truths do not understand the Buddha's profound truth." - MMK 24.8-9

In my understanding of the Mahayana, it is a crucial point of practice to realize that the ultimate is not beyond this world, but rather is the true nature of all things such as they are. In this sense, the liberating insight into the nature of reality is often termed 'suchness', or dharmata.

In the Prasangika-Madhyamaka interpretation of Madhyamaka, all phenomena exist conventionally, in dependence on their causes and conditions, and in dependence upon being conceptually-designated by a valid consciousness. Ultimate truth refers to the lack of intrinsic identity of all phenomena - that all things are free of identity, arising as a mutually-interpenetrating web of causality and dynamic interaction.

In the Prasangika-Madhyamaka view, ultimate truth is itself a mere conceptual construct, and exists only conventionally.

Whatever is dependently co-arisen, that is explained to be emptiness. That, being a conventional designation, is itself the Middle Way.
MMK 24.18

Also, Nagarjuna teaches "There is not one particle of difference between Samsara and Nirvana." In this sense, the ultimate and conventional truths are different realizations of the same basis, and neither transcends the other.