The Bottomless Pit is not Hell or Hades, the place of abode of the Spirits of wicked men and women until the resurrection of the Wicked Dead.
Neither is it Tartarus the Prison House of the fallen angels in Jude 6-7, nor the Lake of Fire, the final hell in Matthew 25:41.
But it is the place for the demons, who are not Satan's angels but a group of disembodied spirits. They are wicked, unclean, vicious and have power to derange both mind and body.
They are Familiar Spirits and the Seducing Spirits that Paul warned Timothy about in 1 Timothy 4:1.