The second layer of Baator is a burning city of iron. The red glow of infernal heat burns within the scorched iron walls, and a pall of smoke rises up to form a general dark haze over the entire layer. For the city is the layer and the layer is the city, Dis. Some claim that a traveler who walks far enough can leave the city behind, concealed within a great ring of mountains. Ranks of red, glowing buildings extend to every horizon, rising and falling according to the hidden terrain. Palatial mansions of particularly important devils and officers of the Blood War break the cityscape here and there. Every iron wall glows with heat, and casual contact with the walls deals 1d6 points of fire damage. Even the iron cobblestones glow with heat. Without iron-shod boots, visitors soon writhe and burn in the streets. Screaming petitioners, captives from the Blood War, and mortals kidnapped from the Material Plane fill subterranean prisons beneath the streets. The sound of their agonized lament is usually audible from small vents in the city walls. Some sections of the city host markets and bazaars where creatures from a variety of different planes meet. Most seek to buy or sell questionable wares, or hire a bloodthirsty band of mercenaries for work that only a devil could love. Crowds fill the streets. Parades of devilish nobility attended by lemures and horribly sculpted soul shells vie with countless work gangs who constantly sally forth to repair, extend, or remodel the city at the behest of Dispater, Lord of the Second.
The Iron Tower is visible from every part of Dis, for it reaches high above the city, piercing the haze of the layer. The tower's form seems to constantly shimmer and change textures and architectural styles. The Iron Tower is Dispater's personal redoubt. Within its walls, he enjoys a +20 bonus to his Armor Class, spell resistance, and all saving throws. He is almost invulnerable there, so he rarely ventures forth, preferring to lead through erinyes messengers.
There's a little-known region of the Iron City that most people are not aware of. Those of you who wish to give the Baatezu the laugh after signing a contract with them should consider this. Debtor's Prison is the name given to the holding area reserved for those pathetic sods who got scragged by the Baatezu. Little did they realize at the time that they were building an interest that they could never pay off by any conventional means. The Baatezu jokingly refer to this complex as "Cell Block 6."
Cell Block 6 houses the unfortunates that just didn't have the talent to outwit the fiends at their own game. "Residents" of Cell Block 6 are stripped of all clothing and confined in overcrowded rooms for hours at a time. The searing heat of the iron walls burns deeply into the flesh and spirits of the imprisoned fools. This is just one of the many delights the Baatezu have in store for the worst offenders.
Cell Block 6 houses one of the largest torture facilities in the Iron City. Here, the screams of the transgressors are muffled by the screams of the naked prisoners being slowly cooked by the walls and floors of their "group meeting" cells. The Baatezu don't even worry about any Schadenfreude that may develop since they debts being paid by the victims is painful enough to block out everyone else. In fact, the poor berks scramble to sit on each other in order to escape the pain of the burning metal. The Baatezu watch carefully to ensure that none of the prisoners are actually killed, since that would be too easy of a way out of their debt.
In addition to these torture rooms, the Baatezu have "research" rooms which are little more than torture rooms in their own right. As part of their debt to the Baatorian society, those fortunate, or unfortunate, enough to be the focus of Baatezu experiments have their bodies changed in some form or another. A few have been horribly disfigured just to see what the reaction would be from the victim's fellow inmates.
Survivors of Debtor's Prison rarely talk about the horrors they experienced. From what little I was allowed to observe, there's good reason not to. I'd rather be sent to the front lines of the Blood War naked and unarmed than confined to Cell Block 6 in the Iron City. No matter how horrible Debtor's Prison may be, those confined knew the price well in advance for the course they have chosen.