Here is the more detailed description
Imagine, if you will, a massive, nation-sized hedge of thorns.
This is our world. The Vale of Thorns.
The Vale is completely covered in these thorns, except for the roseways, petal-covered roads that serve as the arteries between the Vale's major settlements, and the glades, open patches of land where both settlements and dungeons can be found. All settlements are in a glade of some sort, but not all glades contain settlements. Some hold abandoned structures, some have entrances to the Labyrinth and some have nothing but open land. The Thorns cover everything else.
The Thorns take up most of the space in the Vale. In most places they stand some thirty feet high, thick, dense hedges of razor sharp needles. Each and every one is a paragon, a perfect example of what a thorn hedge should be. Despite their wicked barbs, the Thorns are beautiful, and can captivate and ensnare an unprepared traveller. The emotion they inspire within others is their greatest danger; even if a victim is not torn to pieces by the Thorns he may lose his mind and become their slave, or be drawn into their midst and become unable to find his way home.
The Labyrinth used to be a massive city, the name of which has since been lost to history. Some time though, millenia ago, the city became buried, and the Thorns grew out of the ground covering it. Now, the Labyrinth is an undead-infested deathtrap. Some people try and use it to traverse the Vale, since most remaining entrances to the Labyrinth are located in glades or settlements, but most usually succumb to the seemingly limitless hordes of undead, and then join them.
As to the World Forest: you ever hear of the Mists of Ravenloft? Okay, the World Forest is a meeting place for the Mists. The Forest isn't technically a fixed place, it's a gateway to other times and places, a way to travel in time or get to entirely different worlds. Of course there's no way to properly control where and when you'll end up in: you go into the Forest and wander out into some other forest, but it's another age or another place, or both. The forest of Grimmendeep, located on the Vale's northern border, is our way into the Forest; every where else the Thorns border us in.
In pretty much the center of the Vale lies the Thornspire, a massive, snow-capped mountain, that is home to the dwarves who occupy the dual settlement of Tradegate on the slopes and The Delve inside the mountain itself. The Thornspire is also unique in that it has no entrances to the Labyrinth, unlike other underground locations in the Vale.
East of the Thornspire lies Firepoint, the largest city in the Vale. Virtually all the races of the Vale congregate here, in this city where it never stops raining. The city is a sprawling urban mix of architecture from all over the Vale, and perhaps some from outside of the Vale. It's dually ruled by its Duchess, Ekaterina Lursis, who is ostensibly the leader, and the mysterious assassin Miss Cutter, who runs the day-to-day affairs of the city. Firepoint is a hub of industry and trade as well. You can get almost anything there.
Further east of Firepoint lies the newly founded city of Narsopath. Built by the shadar-kai after they razed the eladrin city of Lunaer, the city is still under construction, but already bears an aura of tyranny and hatred. A few smaller shadar-kai settlements lie to the north of Narsopath. I have yet to name these settlements, but this is where the invading army that destroyed Lunaer and founded Narsopath came from.
West of the Thornspire lies the hidden city of Illaya’Fae, a dryad ruled city of fey. Most of the citizens are eladrin or elves.
South of the Thornspire lies Garndall, a former eladrin city-state, now the home of the halflings, who are protected by the dragonborn. Garndall is the Vale's center of agriculture, just as the Thornspire is the Vale's source of stone and metal.
Far to the north of Firepoint lies the Grimmendeep Forest, which feeds directly into the World Forest. Here lies the village of Heathfast, and far to the north of that, the elven city of Naissus, where lumber, leather and ivory come from. Beyond Naissus, Grimmendeep bleeds into the World Forest.
Somewhere to the west of Naissus, outside Grimmendeep, squats Ugluk, an ugly city inhabited by goblins, orcs, hobgoblins, minotaurs and the like. They are, for the most part, civilized, compared to their kin who roam the Vale like bandits or attach themselves to petty masters of evil. They trade with the other city-states, and are cordial in diplomacy, but no one trusts a monster from Ugluk anymore than one from anywhere else.
A number of smaller villages dot the glades between these major cities, Heathfast being one example, as well as others like Duncott and Wraithwater.
There are a few rivers in the Vale, one of them leading to the Midnight Sea, which leads to a separate world called the Void, where there is no sun, and it is always night.
Now, here's the Vale's history (nobody in the campaign's memory goes back this far:
Once upon a time, all that existed in creation was the World Forest and, in it's centre, the vast ancient city. At this stage the Shadowfell and the Feywild were seperate from the world; basically, everything was as is set out the DM's Guide, as regard to the planes. And the World Forest was just a normal forest. Very big, granted, as it covered the whole world apart from the ancient city, but nothing apart from trees.
Above the city hung a massive earthmote, plucked from the Elemental Chaos itself. But then the earthmote fell, and the world was torn apart. Bits of the city weren't even sunk, but sent off to crash into other worlds (like the one in the DM's Guide. All the ruins there: actually bits of the ancient city). The stuff that wasn't blasted out of the Vale was sunk below the surface and turned into the Labyrinth.
The collision also sent magic washing over everything - this earthmote was ****ing HUGE, the biggest ever. A wraith named Avock took a huge dose of it and became the master of dreams, the World Forest took another huge dose. and became the meeting point for dreams and the Mists. And the two planes closest connected to the Vale, the Shadowfell and the Feywild, where smashed together, creating the Thorns and the glades. Other bits of the magic went into Naissus and the Thornspire (the Thornspire is what's left of the earthmote after it landed), and still other bits following those chunks of the ancient city to other worlds.
So, right now we have the Shadowfell and the Feywild that are both connected to the Vale (as per the DM's Guide), but also are part of it. Theoretically speaking you could accidentally wander into one of these other planes just by taking a wrong turn on a roseway, though at the same time rituals designed to travel from plane to plane still work the same. The Astral Sea, Abyss, Hells and Elemental Chaos are all in their normal places because they weren't as connected to the Vale.
The World Forest/Forest of Dreams is actually a separate plane, just like the Astral Sea or whatever. It's just quite easy to get into, like heading north from Grimmendeep (obviously there are other ways in on different worlds, but we'll invent those when we need to). The only reason that no-one else is going into it is because only the vistani know about it, and they don't tell anyone else. The elves from Naissus might know about it too, but they're wiser than to go in themselves; they've know all too well that those who go in don't tend to come back out.
The vistani though, can navigate the Mists. If you manage to persuade them to serve as guides through the Mists, you can exit the World Forest when and where you want. But getting a vistani to guide you through the Mists is very difficult, and very expensive. It's the main advantage they have over all the other races and thus not a secret they part with readily.
The vistani refer to the World Forest as the Forest of Dreams, because, unknown to other people, the Forest is where dreams reside. It's a twilight place, pitch black but lit by endlessly burning lanterns hung from the trees here and there.
Only the dead dream: the thoughts of the souls of dead creatures float away to the Forest and congregate, and then float on to the sleeping living and are breathed in. When the sleeping living wake, the dreams leave their body and return to the Forest to await another sleeper. So, when you wander the Forest, you can bump into dreams, floating eerily through the Mists that coat the ground.
Somewhere within the Forest is the cottage of Avock, the master of dreams. Avock has existed for aeons, even back when the gods were at war with the primordials. Of course he wasn't the being of power he is now, but he absorbed most of the raw energy that was washed over the Vale when that earthmote hit the place.
A couple of worlds we already have in mind is the one in the DM's Guide, and the one that leads on to the jetty on the Midnight Sea, which we can cross to get to the Void (that place where it's always night-time).
And that's pretty much everything we have at the moment. Enough info?