In Classical times, the underworld was a dump for all the culture's worries (note the list of undesirable abstractions and monstrosities located by Virgil at "the jaws of Orcus"); and because everybody ended up there, it wasn't a designated place of torment. It was merely a shadowy and unpleasant realm, a bit chaotic because everyone ended up there.
Even Virgil, however, includes a few particular punishments for a few special cases: former mortals who offended the gods (usually perfectly justifiable given the provocations from the gods in the first place). Ixion swirls forever, strapped to a large wheel. Sisyphus rolls a boulder up a hill endlessly. Tantalus tries to reach for fruit and the branch jerks away; he tries to sip the water that surrounds him but it recedes. And some groups have special torments: trying forever to carry water in sieves, or having rocks continually suspended above, about to fall.
Numerous visions of heaven and hell circulated in literary form before Dante, as the Western world became christianized, and the punishments and rewards were meted out in accord with the religious dogma. But these are still pretty chaotic depictions of Hell.
Dante's Hell is not chaos but a well-oiled machine. This accords with the medieval mania for scholasticism and prompts Dante to envision a system of Hell presented in a tight poetic pattern (the "terza rima" -- the interwoven rhyme scheme threading together stanzas of three lines each). Hell then is a gigantic system whose structure and elaborate subdivisions all make absolute mathematical sense. (So now randomness seems to be the real threat.) Of course, if there is beauty in order, then where is the hell in this? Does Inferno become something it doesn't want to be?
Why go to hell? One can interview the dead, and they usually know more about life than the living, or at least have a useful perspective. But Dante's journey is not just that, nor just an encyclopedia of arcana, nor just proto-science-fiction in a strange geography, nor just a sightseeing tour. This is also an autobiography of the soul.
Now, for a Canto by Canto discussion, we go to hell.