The Manual of the Planes took adventurers from the worlds they thought they knew into cosmic fantasy that spanned an entire planarscape. Come take a look at the first edition of this monumental book.
D&D does many things well–from establishing heroes of unlikely race and class combinations, to filling 10×10 rooms with orcs and/or pie. But it really shines at that moment when player characters become powerful enough to venture past their reality and explore the cosmos, which is full of strange and wondrous creatures that will absolutely try and kill you.
Today we’re taking a look at the Manual of the Planes. First published in 1987, the Manual of the Planes lays out the cosmology of the D&D universe. Starting with the Prime Material Plane in the center of it all, bordered by the Inner Planes, which are themselves bordered by the Outer Planes. A great way of thinking of these is the Inner Planes are sources of power and places where planar functions happen, while the Outer Planes are destinations. So in the Inner Planes you’ll get the elemental and quasi-elemental and demi-elemental planes of existence. Things like the Plane of Fire and where it intersects with the other elemental planes, things like the Plane of Smoke.
After all, those Mephits gotta come from somewhere. And back in 1st Edition, you still had the Positive and Negative Energy planes (which stuck around through 3.x at least). All of these planes were hostile to life without some kind of protection–typically available by magic.
The Outer Planes, on the other hand, are your destinations and afterlife playgrounds. Things like the Nine Hells or the Seven Heavens are all found here. But then in between is where D&D gets delightfully weird. That Astral Dreadnought up there (who would go on to inpsire the Cacodemon out of Doom) is one of the massive creatures that lurks in the space between the planes. Astral travel, movement to and from the Border Ethereal, this is where D&D gets cosmic. Where you run into creatures that are not quite gods, but approach them in a meaningful way.
Where you get into strange journeys that are almost a rite of passage in any D&D player’s career. There comes a moment where you step out onto the Planes and realize you can go anywhere. And that’s when a Dreadnought comes to make the DM’s life easier and gently discourage that from happening all the time.
At any rate, you can read more about the planes in 5th Edition in Mordenkainen’s Tome of Foes!