The attraction to PS! DUDE! You're kidding, right?!
Okay, think London circa 1800's. Rainy, polluted, british accents everywhere.
Now, add a healthy dose of NYC-style diversity and class structure, with rich, wealthy bigwigs and the wild and varied cultures, people, and styles.
Twist it a bit. Include, say, a celestial getting a drink at a pub. A bar that caters specifically to demon tastes (and what it would be like to have a bar whose signiture drink is distilled souls of innocencts). A workshop run by a strange, centauroid ant. A slaad-bar, serving vegetarian meals...or not.
Add a bit of spice in the form of ideas. Lots of ideas, all of them true and none of them right, all at the same time. Don't concern yourself so much with Good and Evil (since one can so easily blend to the other), but be concerned about, say, policemen who beleive in universal peace and harmony if they have to beat it out of you, or lawyers who do nothing but look for loopholes in the very laws that govern reality, or a gym for training monks who beleive that thought gets in the way, and action is all that matters. Put in a group that believes that the entire universe must be sensed, a group that believe that they are all dreaming reality, and a group or two dedicated to bringing them all crashing down (or, in one form, dedicated to bringing any organization crashing down, or not, or whatever, as dictated by Chaos).
You've got the main city (or a good chunk of it). Of course, this isn't taking into account that the main city is a big doughnut floating on top of an infinately tall mountain, ruled by a spectral, pseudo-mythical figure known as the Lady of Pain, interviening only to cause mysterious dissapearances.
And that's just the beginning.
From this locale, sweeping out in all directions, is an infinite number of infinities, cascading lands whose air, earth, and populations are built not from flesh and bones to house a brain, but from ideas that built flesh and bones around them. Philosophy becomes reality as you walk in the lands of the gods of legend, just to see what it's like.
Have you seen the gilded heavens of Celestia? Have you suped with balors in the 90157582097th layer of the Abyss? Have you ever tried holding a conversation with a living, breathing math formula?
...Have you ever truly lived, on that quaint little rock, with it's dragons and it's giants, and it's all-powerful wizard-type?
Come to Planescape, and live.
--Round. And. Round.--
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