As the devils explore Hell, they find that it is pretty much like the one described in Greek mythology, with four rivers (Styx and so on) flowing through it. It is encircled by the river of forgetfulness, Lethe, and beyond that there is a region of constant frost and snow, where the devils are periodically cast into, to make their misery even greater (and wreck their face capillaries). They try to take a sip from Lethe, but it is guarded by Medusa and the water shrinks from them like the water which tortured Tantalus. In the meantime, Satan flies over Hell and finally reaches its gates, where two shapes are crouching (the Helpful Footnote informs us they are Sin and Death). Sin is a little bit like ancient Scylla but much uglier. From the waist up she’s a pretty woman, but from the waist down she is a serpent with a deadly sting, with a pack of hell hounds around her waist, constantly barking, but sometimes creeping into her womb (not sure how if she’s a serpent from the waist down, but let’s not be too literal) and their barking can be heard even from there.