Nirvana is just samsara rightly seen.

The Buddha said in Kalaka Sutta, "When cognizing what is to be cognized, he doesn't construe an

[object as] cognized. He doesn't construe an uncognized. He doesn't

construe an [object] to-be-cognized. He doesn't construe a cognizer.

Thus, monks, the Tathagata — being the same with regard to all

phenomena that can be seen, heard, sensed, & cognized — is 'Such.'

And I tell you: There's no other 'Such' higher or more sublime.

"That saṁsāra is nirvāṇa is a major tenet of Mahāyāna philosophy. "Nothing of saṁsāra is different from nirvāṇa, nothing of nirvāṇa is different from saṁsāra. That which is the limit of nirvāṇa is also the limit of saṁsāra; there is not the slightest difference between the two." [1] And yet there must be some difference between them, for otherwise no distinction would have been made and there would be no need for two words to describe the same state. So Nāgārjuna also distinguishes them: "That which, taken as causal or dependent, is the process of being born and passing on, is, taken noncausally and beyond all dependence, declared to be nirvāṇa." [2] There is only one reality -- this world, right here -- but this world may be experienced in two different ways. Saṁsāra is the "relative" world as usually experienced, in which "I" dualistically perceive "it" as a collection of objects which interact causally in space and time. Nirvāṇa is the world as it is in itself, nondualistic in that it incorporates both subject and object into a whole which, Mādhyamika insists, cannot be characterized (Chandrakīrti: "Nirvāṇa or Reality is that which is absolved of all thought-construction"), but which Yogācāra nevertheless sometimes calls "Mind" or "Buddhanature," and so forth." – Zen teacher David Loy, https://web.archive.org/.../FULLTEXT/JR-PHIL/david.htm

"as David Loy pointed out, "Nagarjuna never actually claims, as is sometimes thought, that “samsara is nirvana.” Instead, he says that no difference can be found between them. The koti (limit, boundary) of nirvana is the koti of samsara. They are two different ways of experiencing this world. Nirvana is not another realm or dimension but rather the clarity and peace that arise when our mental turmoil ends, because the objects with which we have been identifying are realized to be shunya. Things have no reality of their own that we can cling to, since they arise and pass away according to conditions. Nor can we cling to this truth. The most famous verse in the Karikas (25:24) sums this up magnificently: “Ultimate serenity is the coming-to-rest of all ways of ‘taking’ things, the repose of named things. No truth has been taught by a Buddha for anyone anywhere.”"

It is important to understand that even so called "natural unborn 'space' of all phenomena" is not something that is established to truly exist:

Kyle Dixon:

"As the Mahāprajñāpāramitāśāstra states:

"Outside of the saṃskṛtas [conditioned dharmas], there are no asaṃskṛta [unconditioned dharmas], and the true nature [bhūtalakṣaṇa] of the saṃskṛta is exactly asaṃskṛta. The saṃskṛtas being empty, etc. the asaṃskṛtas themselves are also empty, for the two things are not different. Besides, some people, hearing about the defects of the saṃskṛtadharmas, become attached [abhiniveśante] to the asaṃskṛtadharmas and, as a result of this attachment, develop fetters."

Going on to say that the person who rejects the saṃskṛtas is attached to the asaṃskṛtas by attributing to them the characteristics of non-production [anutpāda], and by the very fact of this attachment those asaṃskṛtas are immediately transformed into saṃskṛtas. Which, as I have pointed out before; is equivalent to the act of turning dharmatā into a dharmin by considering it to be a separate, existent, unconditioned, free-standing nature. It should instead be understood that the very non-arising of conditioned dharmas [saṃskṛtadharmas] is the unconditioned [saṃskṛta] dharmatā. It is an epistemic realization which dispels ignorance by severing the causes and conditions for invalid cognition... not an ontological X that exists on its own (that is what Vedanta teaches).

And so in this vein Nāgārjuna states:
"Neither saṃsāra or nirvāṇa exist; instead, nirvāṇa is the thorough knowledge of saṃsāra"
-- Yuktiṣāṣṭika

Saṃsāra is the result of confusion, nothing is ultimately established in saṃsāra (conditioned phenomena or otherwise)... and if nothing is ultimately established in saṃsāra, saṃsāra is itself never truly established at anytime. If saṃsāra is not established, nirvāṇa is not established. Recognizing the true nature [satyalakṣhaṇa] of saṃsāra, as innately unproduced [anutpāda] is to realize that the allegedly conditioned [saṃskṛta] is a misconception of ignorance, and therefore the conditioned has in fact been unconditioned [asaṃskṛta] from the very beginning. That is awakening to the unconditioned, and that is the awakening which is the doorway to the cessation of suffering.

"Since arising, abiding and perishing are not established,
the conditioned is not established;
since the conditioned is never established,
how can the unconditioned be established?
-- Nāgārjuna

So it is not that there is indeed an unconditioned nirvāṇa which abides apart from conditioned phenomena. The 'unconditioned' is merely knowledge of the actual nature of 'conditioned' phenomena. Phenomena [dharmins] are themselves, in essence, unconditioned, their unconditioned nature is their dharmatā.

"Good son, the term 'unconditioned' is also a word provisionally invented by the First Teacher. Now, if the First Teacher provisionally invented this word, then it is a verbal expression apprehended by imagination. And, if it is a verbal expression apprehended by imagination, then, in the final analysis, such an imagined description does not validate a real thing. Therefore, the unconditioned does not exist."
-- Saṃdhinirmocana Sūtra

This is why nirvāṇa is a cessation; it is the exhaustion of one's ignorance regarding the nature of phenomena. What ceases, is cause for the further arising and proliferation of the very delusion which lends to the misperception of arising, abiding and destruction in conditioned phenomena.

For this reason, nirvāṇa is said to be 'permanent', because due to the exhaustion of cause for the further proliferation of saṃsāra, saṃsāra no longer has any way to arise. However nirvāṇa is also a conventional designation which is only relevant in relation to the delusion of saṃsāra which has been exhausted, and so nirvāṇa is nothing real that exists in itself either, it is merely the absence of affliction, an exhaustion, an unbinding, a release, an extinguishing, a liberation, a cessation... that is nirvāṇa. There is sickness and there is health... health is simply the absence of sickness.

So the correct understanding of phenomena, reveals that phenomena (as misperceived via ignorance) have never occurred in the way one's ignorance made them appear. As a result it is seen that there has never been anything which was bound, nor anything which required liberation. That seeing reveals the unreality of saṃsāra and nirvāṇa as inherent entities, and the definitive and living freedom from saṃsāra [bondage] and nirvāṇa [liberation] is itself liberation.

Eternalism; in the vein of reifying a truly existent ultimate, is never necessary, and is a ridiculous notion.

[11:01 AM, 5/26/2021] Soh Wei Yu: - kyle wrote six years ago

[11:07 AM, 5/26/2021] John Tan: (thumbs up)"