What the Bible says about Bottomless Pit
(From Forerunner Commentary)
The Devil will again go on the offensive against God with the same results: He is cast back down to earth. In his anger over his defeat, he will savagely persecute God's people and gather the armies of man to fight against Christ when He comes. He and his human agents will be soundly defeated, and Satan will be bound in the bottomless pit for a thousand years.
Richard T. Ritenbaugh
Basic Doctrines: Satan's Origin and Destiny