The bliss of nirvana without sensation Some sensations are neither good nor bad, when I think there is an absence both of pleasure and pain.

But what about nirvana itself? Obviously there is no vedana to it. 

Is its "bliss" something like the memory of neutral sensation? 

I just wonder if that's what it's like to be without the three poisons of attachment aversion and ignorance.
A basic answer is, Nirvana is zero attachment and zero aversion. Imagine how you'd feel if you had zero attachments and zero aversions, not even a slightest hint. That is Nirvana.

I'm not sure what the orthodox position says about vedana, but from my perspective it should still have vedana. It is just, when pleasant vedana arises, you see it arising, and when it ceases you see it ceasing. When unpleasant vedana arises, you see it arising, and when it ceases you see it ceasing. No attachment and no aversion - therefore no suffering.

Could you say the absence of suffering is bliss? Yeah, kinda - you could qualify it as a very subtle form of bliss, a #0-thickness bliss.

Have you ever had a dream in which you fly so high that there is nothing left but sky on all sides around you? They say, the experience of dharmakaya is like that. Another comparison I heard from teachers is what astronauts feel on the orbit - constant free fall. It is scary at first, because you feel like you're going to crash - but you can get used to it and even be functional.

So I guess that must be the feeling: the absence of suffering due to attachment/aversion, but also the absence of any kind of comfort you normally get from having some kind of reliable ground. Could we call this the bliss of endless free fall?

Another way to describe Nirvana, is as death of ego. Imagine you have lost everything. All hopes, all promises, all meanings - nothing left. Because you lost your valuables and futures, you have nothing to lose. Because you have nothing to lose, you have nothing to fear. Which makes you into a kind of superman, just a very sober superman, because you no longer get intoxicated or carried away by childish illusions. No hope, no fear. That's another way to see it.

Now combine the two images: the endless free-fall with no grasping onto anything  and no suffering, with no ground, no home, no hope and no fear, everything lost and everything gained, very sober and absolutely stable in infinite agility. That's what they say Nirvana feels like.