"Then death and Hades were thrown into the lake of fire. This is the second death, the lake of fire." (Rev. 20:14)
We do know some things about Hades. It is temporary. At some point, the dead will be taken out of Hades: "…and death and Hades gave up the dead which were in them…" (Rev. 20:13) Whenever we see Hades in Revelation, it is always accompanied by its sidekick, death (Rev. 1:18, 6:8, 20:13, 14). These mysterious and morbid partners are both quite unwanted to the human soul. Truly enemies.
"What man can live and not see death? Can he deliver his soul from the power of Sheol?" (Psalm 89:48)