You can look back at the first Planescape product I wrote alone, Planewalker's Handbook, and see that I've long been interested in devising a cosmology where the planes were not static but their connections changed as they "moved" in a higher dimensional sense. In that book I created a device called the Celestial Etheroscope. My original idea was that one could use it to observe the movements of the planes in the same way that an astrologer looks at the movements of the planets. But planes in the core cosmology decidedly do not move. So the etheroscope was changed to fit with the cosmology better and, in fact, it was still alien enough to the whole planar setup that I think people rarely used it in Planescape campaigns.

But now, with Beyond Countless Doorways, I'm not limited by what's come before. So the cosmology here, called the Countless Worlds, is all about moving planes. Planes move in and out of conjunction and even separate entirely in something called a severance. (See illustration by Ed Bourelle; click for a larger image.)

Planes in conjunction are "close together" in a metaphysical sense. It's easier to cross their boundaries with magic -- summonings, portals, and so forth. Planes out of conjunction are farther apart, making such magic more difficult to use. Planes in severance with each other are entirely apart, so it's impossible to travel from one to the other (or to summon things from one to the other, and so on).

However, what commonly happens is what is called a series conjunction. Two planes might be in severance with each other, but each of them might be in conjunction with a mutual third plane. Thus, you can't go from plane A to plane B directly, but you can go from A to C, and then from C to B. DMs can use this idea to create long chains of series conjunctions -- planar pathways, if you will -- required to get from the PCs' current plane to the one they need to visit. To get to Erradin, a plane of fire where they must find the flameheart jewel, the planar travelers might have to travel first to Dark Perador, a parallel world where the sun has grown cold, and from there to Jemath, a hellish plane of acid pits and denizens who feed on pain. From Jemath they must find the only portal that leads to Fatalon, where noble celestials hold court. But they must hurry, for Fatalon does not remain in conjunction with Jemath for long. From Fatalon, the journey to Erradin becomes possible, assuming they are in the good graces of the nobles who maintain complete control of all travel out of their plane.

This, in my mind, is the way true planar adventures are born. It's not a matter of casting plane shift and -- boom -- you're at (or at least near) your destination. Planar travel should be strange and mysterious, as well as arduous and dangerous. A journey to another plane should be a real journey, with challenges along the way as well as once you've arrived.

And this is really only the tip of the iceberg. The Countless Worlds cosmology incorporates the ideas of planar storms moving from one plane to the next, and even planar infections that one plane can catch from coming into conjunction with another. There are planar wardens, who each watch over a single chosen plane, and the Purveyors of Dichotomy, who embody half of one of the many planar opposite pairs: law vs. chaos, fire vs. water, light vs. dark. They gain power as more planes fall under their dominion and away from that of their hated opposites.

But really, the meat of Beyond Countless Doorways are the planes themselves. In coming installments, I'm going to write about some of the specific planes in the book and why we created them the way we did.

DESIGN DIARY PAST ENTRIES

* Designing a Cosmology -- May 20, 2004
"First off, let me say that there's nothing wrong with the Core Cosmology, or, what we used to call the Great Wheel...."

* Keyed Spell Items in Book of Hallowed Might II -- April 15, 2004
"Mike and I did some work recently on Book of Hallowed Might II: Portents and Visions. The Book of Eldritch/Hallowed Might series has been great to me...."

* Legacy of the Dragons: A Monstrous Challenge -- February 26, 2004
"I love new monster books so much, I pretty much never pass one up, no matter what. I wanted Legacy of the Dragons to be friendly to the folks out there who are like me."

* Legacy of the Dragons: Bestiaries I Have Known -- February 19, 2004
"My first professional game design ever was a book of monsters. Creatures and Treasures II came out in 1989 from Iron Crown Enterprises for Rolemaster..."

* Legacy of the Dragons: Context -- January 22, 2004
"Legacy of the Dragons is the product I'm working on now. Just finishing it up, actually. It's a bestiary to go along with Monte Cook's Arcana Unearthed...."

* Chaositech Playtesting -- December 11, 2003
"Chaositech is one of those products that came directly out of my campaign. The concept was not meant originally to have anything to do with a product...."

* Campaign Paradigms -- October 30, 2003
"An important thing for all DMs to keep in mind is that once a campaign is up and running, the basic flavor -- the underpinnings of the whole campaign structure -- usually should not change...."

* Developing a New Subsystem -- October 2, 2003
"Probably one of the biggest challenges that faces a designer when working on a book like Chaositech is the delicate way that you have to institute a whole new subsystem...."

* On the Horizon: Chaositech -- September 11, 2003
"If you'll indulge me, I'm going to divert the Design Diary's contents to what I'm working on now: a book called Chaositech...."

* Magic Items in The Diamond Throne -- August 28, 2003
"Magic items in Monte Cook's Arcana Unearthed and in The Diamond Throne sometimes require a little bit of thought on the DM's part. Using them isn't a problem..."

* A Look at the Land -- August 15, 2003
"This week I've prepared an excerpt from The Diamond Throne. As I've said previously, it was my design choice to spend most of the gazetteer portion of the book on the general aspects of the world..."

* Designing a World -- August 7, 2003
"I have mixed feelings about campaign settings. On one hand -- speaking as designer -- it's fun, challenging, and rewarding to create a whole world that's all your own...."

* Weapons and Armor -- July 17, 2003
"I absolutely love the introduction of exotic weapons into D&D. It's one of my favorite things about 3rd Edition. In Arcana Unearthed, I wanted to make sure that the exotic weapons were worth the feat required to use them...."

* Greenbond Notes -- June 26, 2003
"Last week's preview of the greenbond class gives a nice glimpse of a lot of Arcana Unearthed issues. First off, the greenbond is no druid...."

* Spell Templates -- June 12, 2003
"This week I thought I'd discuss an idea that I'm really very happy with. The idea is spell templates..."

* Playtesting -- June 5, 2003
"Playtesting is extremely important to me. When we developed 3rd Edition, we did more playtesting than perhaps any other RPG product, ever...."

* High Magic -- May 29, 2003
"I referred to the Diamond Throne as a high-magic setting. I should clarify..."

* The Diamond Throne -- May 23, 2003
"So it's about time I start talking about the Diamond Throne. The Diamond Throne is a campaign setting for Arcana Unearthed -- the default setting, like Greyhawk for D&D, I suppose...."

* Death's Door -- May 8 , 2003
" I like the D&D death's door rules. I like that at 0 hp, you're still up and can take a limited action, but then you exhaust yourself...."

* Hero Points -- May 1, 2003
"A roleplaying campaign can be like putting up wallpaper...."

* Truenames -- April 18, 2003
"Truenames are common in many fantasy settings. I think I first became aware of the concept in Ursula K. LeGuin's Earthsea trilogy..."

* Go, Go, Go! -- April 10, 2003
"Short entry this time. I hate spells with 1 minute/level durations...."

* Ceremony -- April 3, 2003
"I think I've already mentioned that one of the goals I set for myself with Arcana Unearthed was to make things a little less generic...."

* Things That Rules Take Away -- March 21, 2003
"There are aspects of fantasy roleplaying that rules, inadvertently, can actually take away...."

* Still Talking Classes -- March 13, 2003
"I've saved some of the best classes for last. Let's talk about the runethane, the mage blade, and the witch...."

* More Classes -- February 27, 2003
"This time, I want to tell you about some of the other classes: akashics, magisters, and greenbonds...."

* Build a Better Fighter -- February 23, 2003
"The title this week is facetious. It really should be 'build a different fighter'...."

* The Magic Balancing Act -- February 13, 2003
"In Arcana Unearthed I'm introducing a new method of magic item pricing. First, I streamlined the item creation feats..."

* More Magic -- January 23, 2003
"This week, I thought I'd talk more about the new magic system in Arcana Unearthed."

* Magic -- January 17, 2003
"As a designer, magic in Arcana Unearthed posed a huge challenge. I knew that I wanted to ditch the Vancian system...."

* Design Decisions, Part Two -- December 24, 2002
"Here's a bit more discussion of some of the general issues I faced as I began designing Arcana Unearthed...."

* Design Decisions, Part One -- December 19, 2002
"Before jumping into another big area of Arcana Unearthed's design, like classes or the magic system, I thought I'd discuss some of the general issues I faced as a designer starting the book...."

* Arcana Unearthed Races -- December 5, 2002
"I started with the races. While I knew that the game needed humans as a basis, I wanted all the other races to be new. I didn't want to just create dwarf and elf analogs with different names...."