Hades is the Greek part of the Underworld. Elspeth, Cleo and Flora enter the Hades portion of the Underworld in Episode Three through a secret passage in the cellar of the Strawberry Fields bar.
The passage down is pitch black but everything is illuminated by a ghostly green light. Swamp water lies between jagged stones that form a path with tufts of grass in places. It feels cold and clammy. Across the marsh are green specters, wandering. There is a towering obsidian wall with an unlocked gate guarded by Kerberos. The path continues for a while until it reaches a jetty at the River Styx, where Charon stands to row people across. Rising up in the distance is a large obsidian castle.