firewrns is right. Upon the death of an Arahant, he/she is not born in this world of 31 realms. He/she merges with Nibbana. Qualities of Nibbana cannot be explained in terms of our vocabulary because IT DOES NOT belong to this world. But it is a permanent state without any suffering.
Suffering is present in each and every realm in this world, but it is hard for normal humans to understand. That is why the Path has to be followed step-by-step without getting hang up in definitions. Just try to understand concepts at ones’ own level. I have no idea what level of understanding each person is at.
Here is the step-by-step process:
One needs to get rid of the 10 types miccha ditthi first. Then one needs to start comprehending Tilakkhana, and when one starts seeing “the futilty of existence in any realm” one attains the Sotapanna stage. Only after that one can see overcome the desries for sense pleasures and get to the Sakadagami/Anagami stages. Only at that time, one can fully comprehend that even those higher realms are filled with suffering.
I suggest carefully reading the following two posts:
“Nibbāna – Is it Difficult to Understand?” (Especially see #7)
Is It Necessary for a Buddhist to Eliminate Sensual Desires?
More posts on Nibbana at: