Touched on it as the place of the dead, the place of demons, the dangerous place of great knowledge where you must quest.
One writer explained how a first reader told her she had to send her characteres into the Underworld and dang if that wasn't just what the novel needed.
One brought up Liz William's Inspector Chen series where Inspector Chen has a partner who was a demon, and had worked for Hell's Vice Squad and consequently has to remind himself that on earth, the Vice Squad has a rather different purpose.
One panelist explained the "Lyke Wake Dirge" as a journey to the Afterlife, and despite its refrain "And Christ receive your soul" said it wasn't very Christian. (I differ a bit: it tells you how to escape the perils, and its recommendations are exactly those of the Parable of the Sheep and the Goats: alms-giving.)
One audience member recommended Groundhog Day as being trapped in an Underworld, and a panelist thanked him because people keep recommending it to her as a romantic comedy, but knowing its a story about being trapped in the Underworld is just the spur to get her to watch it.
Someone in the audience told about a twentieth century novel that used Hell for social satire and asked when it was switched from being serious; whereupon someone told him about The Frogs which is an ancient play using Hades to satirize that era's play-writing, and all the panelists agreed that it was used for satire probably from day one.