The Void

The Void is a cosmic realm of nonexistence, sometimes referred to as an anti-existence

Trespassing into the void means annihilation, regardless of the trespassers power or capabilities, the way the Void annihilates it's visitors is by targeting their very existence by erasing any memory of them, their entire past, even their very soul as well as every result of their existence, effectively making them never having existed in the first place.