Something which cannot be experienced [closed]

In philosophy, if something is transcendent, it's not realizable in human experience.

Unknowable.

Note the word experience used in this definition by Merriam-Webster Dictionary:

unknowable : not knowable; especially : lying beyond the limits of human experience or understanding

https://www.merriam-webster.com/dictionary/unknowable

Here are some others depending on your intent. I'm providing all of these because it was not clear from your question if you wanted something philosophical or concrete.

unattainable

not able to be reached or achieved.

impossible

not able to occur, exist, or be done.

impracticable

impossible in practice to do or carry out.

Transcendent was already mentioned (a great option if the intent is to be philosophical or metaphorical)

inimitable

so good or unusual as to be impossible to copy; unique.

incomparable

without an equal in quality or extent; matchless.

nonpareil

having no match or equal; unrivaled.

unparalleled

having no parallel or equal; exceptional.

Source Material for all entries: Oxford Living Dictionaries