Where is Abaddon?

Abaddon —  or destruction in Hebrew.  This  is regarded as the  personification of the idea of destruction, or as sheol, i.e. the realm of the dead.

11 The king who ruled them was the angel from the bottomless pit. In Hebrew he is called Abaddon, in Greek he is called Apollyon.”

 Revelations 9:11, Names of God Bible