Kashyyyk appears like any other forested planet: green with trees, blue with water, white with clouds. On closer inspection, the cloud seems more like fog, with the tallest trees poking out. This is an optical illusion; the oldest wroshyr trees stand several kilometers tall, their roots lost in the impenetrable gloom far below. The home planet of the Wookiees, Kashyyyk boasts one of the most unusual and lethal ecosystems in the galaxy. Awe-inspiring wroshyr trees cover its surface, stretching kilometers from the sheltered surface to its wispy cloud layer. The cutthroat struggle for survival began eons ago on the planet's surface; species that could climb higher, such as the ancestors of Wookiees, did so. The creatures that remained either evolved deadly defenses or became extinct. The survivors now thrive in the towering wroshyr trees, and the peculiar plants and animals fill every possible niche in the vertical environment.

Cities are nowhere to be seen until one gets much closer. Then, tiny specks appear through the haze of smoke: the network of towers and bridges and the pale, flat discs of landing pads cut from single limbs of the titanic wroshyrs. Closer still, individual buildings, sometimes two or three stories tall, begin to stand out, as do the wide, flat streets between them. The immensity of the physics becomes wondrously clear: each city is built on interwoven branches so large that a ship could land on the cross-section, so sturdy they stir only in the most intense winds. Kashyyyk's cities are built in conjunction with nature, not in spite of it, and yet they are fully functional cities, not crude villages or simple structures. Technology and nature blend everywhere, in the speeders cruising along limbs as wide as multi-lane highways, in the organic exhaust ports of the computer-component factories, and in the grand crystalline windows of the mansions, museums, and temples. Kashyyyk is far from primitive; it is simply natural.

The steamy temperatures in Kashyyyk's swamps and inland lakes cause a tremendous amount of humidity. Most water vapor rarely rises more than a kilometer above the ground before it is trapped by foliage, where it condenses and falls back into the water table as dark, soil-rich rain. What evaporation occurs on the upper levels makes for light cloud cover and periodic light rainfall. Windstorms are infrequent, and usually not very strong - certainly not strong enough to shake the treetops. Lightning is extremely unusual on Kashyyyk, as the wood of wroshyr trees is an insulator against negative electrical build-up.

Kashyyyk's geographical regions are broken down more by climate and terrain, and less by geopolitical boundaries. The most populous regions are the central northern and southern hemispheres, where the temperatures are more comfortable. The population drops off as the temperatures rise toward the equator and drops toward the poles. The seas are, of course, uninhabited by Wookiees, who are not comfortable that close to the surface, dry land or not. Each of Kashyyyk's four hemispheres are partially inhabited with at least one major city. The largest cities include Truvvhhurr, Kamarkiia, Hoorrkhukk, Maarwraawroo, and Rwookrrorro, all of which are built around manufacturing facilities that provide Kashyyyk with trade goods for offworld commerce. Smaller communities, such as Kroohhuhwoor, Orriorr, and Rarrhkrrorrho, tend to focus on agricultural goods sold on Kashyyyk itself. Most tend to think of Kashyyyk as covered in wroshyr trees, as land without tree growth accounts for only three percent of Kashyyyk's surface, but the surface of Kashyyyk is almost 40% water. Even on Kashyyyk's seas, there is a considerable amount of tree cover far, far above.

The Wookiees divide the wroshyr forests into seven vertical levels. The upper canopy is occupied by the Wookiees, and it is further subdivided into the highest level (the nursery ring, where Wookiee children are minded and educated while their parents work), the habitation level (where Wookiee families dwell and work), and the maintenance level (where most Wookiee public utilities are located, including sewage and power generation).

As one travels farther down, it becomes increasingly more dangerous. A few predators exist on the level directly below the Wookiees' level, but these are small and easily circumvented. On the third level down, carnivorous syren plants exist in massive numbers and sizes. Below this level, things swiftly turn lethal. The fourth level down is inhabited by deadly predators, to whom a full-grown Wookiee warrior is little more than a passing challenge.

The next two levels are known as the Shadow Forest, the part of the forest too far below the canopy for light to penetrate. This is the domain of the webweavers, giant, spiderlike creatures capable of devouring the most powerful Wookiee in a single bite. The Shadow Forest is a colossal maze of adhesive webs, where the slightest tremor attracts the attention of the webweavers. Finally, the ground level is given over to swamps, inland lakes, and sluggish rivers. The fauna at this level is more strange than lethal (though there is a fair amount of the latter), and most of the creatures live in complete darkness broken only by the occasional patch of phosphorescent flora. A few creatures provide their own illumination, which usually attracts the attention of ground-level predators, so these creatures are either prolific or extremely dangerous in their own right. Wookiee legends tell of gigantic monsters that prowl the deepest reaches of Kashyyyk's mighty forests, and the Wookiees know all too well that those legends are grounded in perilous truth. Those few Wookiees who travel down this far below rarely return.