Mongoose D20 book for 3.5 book of planes. Most of the content is fairly system agnostic, not particularly crunchy. It is important to note these are not the Outer Planes of AD&D (Abyss, Nine Hells, Shape Creature Place) but stuff developed by Mongoose. There is also a toolkit for generating planes.
Go beyond the fields we know, into the realms of high fantasy and legend. The planes are a far grander stage for adventure than the mundane wilderness and dungeons of the world. Out there, the characters can walk with the gods themselves, delve into the foundations of the cosmos or quest in the lands of the dead or be the deciding factor in the great wars of Good and Evil.
This is truly a place for heroes.
Classic Play – The Book of the Planes describes the myriad planes of existence in exacting detail, offering encounters, hazards and adventures in dozens of alternative worlds. Beginning with the elemental planes of Earth, Air, Fire and Water, travel outwards through the transitive Ethereal, Shadow and the Dream planes to the wild planes of Positive and Negative energy. Beyond them, the wide gulf of the Astral plane and the vast Outer Planes.
Presented within are ten entirely new outer planes, along with suggestions for how to arrange and integrate them into your campaign cosmology including the dark realm known as Mâl, where ancient horrors are awakening and the Questing Grounds, the realm of living stories. Including rules for each of these planes, according to a set of magical traits, along with the secrets of the art of Planecrafting, characters can shape their own home plane or wreak havoc by changing the laws of reality.
Travellers do not walk the planes alone, however, there are all sorts of fellow travellers out there, including reality-spanning organisations with their own agendas and conspiracies. Along with advice and new magic for travelling the planes, the wise traveller will consider using one of the Nexus planes; pocket worlds that share boarders with a multitude of other planes.
This tome tackles the mind-boggling complexity of the planes and travel throughout them head on and makes it as simple as fighting off kobolds.
Author Gareth Hanrahan
Publisher Mongoose Publishing
Publish date 2004