Hell is often considered a place of eternal torment (fire, pain, etc.), but that’s not the hell Jesus descends into in the Apostles Creed. That’s characterized in the Catechism as being where the are without God. My thought (that I think is consistent with scripture, at least I’ve found no contraindications yet) is that Hell is simply all that is not Heaven or Earth or Purgatory. The suffering comes from the knowledge of Heaven with no means of getting for, like, ever.