And we reach the final post that will be lifted from the ENWorld forums! Out of all the information brought from that place, this post probably edited the least, but it should still be useful information.
There are nine planes of hell, with eight of them designed to be afterlives for mortals, and one a pocket dimension that exists outside of the Astral Sea. The nine hells can be seen as planets in the Astral sea, and most of the hells appear very Aarn-like, but with different continents. The exceptions are Bureaucracy, Meh, and Revelry, which have their own unique looks.
Bureaucracy - The home of the demons, and the first plane of hell. Bureaucracy was not designed to be an afterlife, and was instead supposed to be the demons' home. As such, it has with it their style of civilization and their style of laws, described in detail in the "Creatures: Demons" post. The plane itself appears to be a massive city which has no day or night; Bureaucracy's weather is gray clouds that constantly glow and give off light. The only time the plane is ever dark is when it rains. This of course means that the other planes and the rest of the astral sea are not visible from Bureaucracy - but the demons still have technology that allows them to observe it all, including Aarn itself as well. The glowing clouds are more for the sake of the demons' own privacy than anything else.
Of course, for anyone living here, a great deal of paperwork needs to be filled out on a day-to-day basis, which makes it extremely difficult for non-demons to live here. Many native Aarnian mortals are absolutely horrified at any prospect of this hell, and the demons themselves are also loathe to allow mortals to spend their afterlife in their own home town. Occasionally though, there are especially shrewd and bureaucratically minded mortals (dragons, for instance) who fit in just fine, and are allowed to stay here.
Paranoia - The second level of hell, Paranoia was originally supposed to be a carbon copy of the real world, to allow those who did not want their lives to change to continue to exist as they always had. Unfortunately, the demons did their job designing this plane too well, and it was too much like the world of Aarn. Very quickly, a system of corruption and political dominance sprang up and began to oppress the populace. The fact that the more violent and "evil" people could not really be killed meant that they instead found themselves in positions of power. This also prevented any would-be revolutionaries from shattering the power structure and loyalty of underlings through assassination.
The entire plane of Paranoia is currently run by an evil empire of criminals and corrupt law enforcement agencies. The only people who can enjoy this hell are narcissistic individuals involved in activities of naked self-interest, who died with a clear conscience over the evils they did in life.
Anarchy - The second plane the demons created for mortal souls, Anarchy is purposefully regulated to prevent mortals from banding together into organized political groups. The demons hoped that this would prevent the problems that plagued Paranoia from plaguing Anarchy. In fact, worse problems developed. Anarchy became an extremely violent place, a constant riot where everyone fights everyone else - except when they're drinking or having sex. There is absolutely no order, no rhyme, no reason to this place. It is an endless sea of strife and chaos. Mass murderers, fighters, warriors and violent predator corporeal creatures tend to enjoy this afterlife quite a bit. Everyone else does not.
Delirium - Delirium is a plane so chaotic that any kind of civilization simply cannot spring up at all. The best way to begin to get a picture of what Delirium is like is to take a herculean dose of peyote, and then give yourself a direct IV drip of pure LSD. Then you have barely scratched the surface of the surreal way Delirium is constructed. The demons created it thinking that the removal of all order completely would allow those who did not enjoy Paranoia or Anarchy to have an happy afterlife.
Those who enjoy Delirium tend to be curious individuals who enjoy sensation for sensation's sake. Otherwise, the plane is just so freakin' bizarre that it is practically impossible for anyone to function at all. From a distance, Delirium appears to be a ball of swirling colors and flashing lights.
Meh - Originally designed to be the final plane of hell, Meh is a plane of absolute nothingness. There is no gravity, no structure, no food, no water, no clothes, and even no bodies. Meh is a place where especially serene and nihilistic people can truly feel like they are at one with everything and nothing. It is also a place that is so boring, so empty, so lacking of stimulus that many call it to be the absolute worst alternative out of all the other eight planes of hell. From a distance, Meh looks very similar to Bureaucracy, though it is not solid and is instead a simple ball of opaque gray gas.
Conformity - After the "failures" of the first four hells, the demons created a plan to construct four more, after studying human nature in more depth. The first of these, conformity is a plane of logic, structure, and technology. The demons populated it with their own robotic creations in order to police the plane and ensure that it ran smoothly. The society itself however is practically nonexistent. People are treated as numbers. There is no such thing as free thought or free expression. People are told what to do, when to do it, and how to do it. Surprisingly, many people actually do enjoy this hell. They are the sort of people who enjoy following a leader, and not having to think for themselves. Strangely, more actual humans populate this plane than any other type of creature.
Security - Like conformity, Security has a rigid authority structure. Unlike conformity, the sensibilities of the populace are actually looked after. Security is essentially the plane of Paranoia run in a tolerable way. Demons called angels are the authority structure here. They ensure that the needs of the populace are met, be they entertainment, food, drink, or other activities. Generally, it is possible to do or receive whatever one wants here, as long as it is not violent, mean, nasty, and does not infringe on the happiness of another individual in any way. In a way it is the ideal gated community.
While this may sound like a paradise, there is a down side. Happiness is regulated. If you are unhappy, you are almost treated as a criminal and taken to a "happiness reeducation center." These centers are often always materialistic in structure and do not tend to address the actual emotional problems causing the unhappiness. Treatment centers are distractions at best, torture at worst.
What is worse, there is absolutely no risk, no thrill, no danger tolerated. Anything that might harm yourself or cause yourself pain is treated as if it were a kind of violence against another person. Even sex, which can often be rough and cause injury is strictly regulated. Keeping these things in mind, it can be easy to understand how this place could be considered a hell.
Serenity - A rustic wilderness with abundant wild food, crystal clear lakes, rains of honey and plenty of fresh air, Serenity is the most peaceful and primal of the nine hells. It is where most herbivore animals go. Philosophers, artists, naturalists, vegetarians and other nonviolent people who enjoy little regulation find this place an utter paradise. The major downside of Serenity is that all there are put under a kind of spell that makes it especially difficult to undergo acts of violence or abuse. The paradise can sometimes be threatened by small spats or fights, but these rarely turn into anything serious. A good analogy for Serenity would be a hippie commune / artist community.
Serenity's major downside is the fact that it can be very boring to those who do not enjoy artistic or intellectual pursuits. While nowhere near as boring as the plane of Meh, Serenity can get on the nerves of those who demand an exciting lifestyle almost as much as Conformity and Security. There is little regulation in Serenity, but it does have just enough to prevent violent thrill-seekers from truly being satisfied.
Revelry - The deepest level of hell, Revelry is a non-stop party. By this point, the demons had gotten so frustrated with their attempts to create suitable afterlives that people could enjoy that they essentially threw their hands up in the air, and decided to provide as much food, drink, music, and other fun things as possible. Extroverts who enjoy fun will absolutely thrive in this place. However, because the party is constant and never lets up, those who do not thrive on social conduct or cannot tolerate too much mindless fun without actual constructive activity will find themselves completely and utterly tortured.
Immigration - While not actually a plane of hell, immigration is a pocket space the demons created to store souls who had yet to be judged. It was supposed to only be temporary, but because of the demons' love of bureaucracy, quite a queue developed at the judgment booth. Immigration is very much like Meh, except it could be considered even worse than that because it was never intended to be a final destination. Immigration is nothing but an endless white space with a snaking line of creatures waiting to be told where they are going. The current wait, from death to judgment, is currently hovering at the equivalent of around 100 years.