Millenia ago, the people of the Valley domesticated an animal known as a cloud spider*. Spider silk is exceptionally lightweight and has extremely high tensile strength, and the humans have been able to tease many uses out of an animal that yields a large quantity of silk.
As humans have done with dogs, cows, etc., the people of the Valley have domesticated the cloud spider and bred multiple variations to suit specific needs. Mostly this is focused on producing different kinds of silk for different purposes, including varieties of silk that can be compacted, hardened, and moulded into all sorts of shapes. The resulting material is extremely durable, lightweight, and flexible. So in place of wood or metal, both of which are relatively scarce, most of their daily-use objects are made of silk.
So yes, the entire structure that houses the country of Pocalo and all its provinces is ONE GIANT SPIDER WEB that has been built up over the course of many thousands of years using construction-grade spider silk. Hence, if you are in any province but the very topmost, when you look up, your view of the sky consists mostly of silk. Hence the name “Valley of the Silk Sky.”
*Don’t worry, arachnophobes, it’s not actually technically a spider! It’s a MONOTREME. There are actual bugs in the Valley, but most of the larger incarnations like the cloud spider are really egg-laying mammals.
The Valley in which the Provinces of Pocalo sit is ringed by a range of high red mountains. The poor nutrient content of the red soil, coupled with the erosion issues on the cloud spider web structure (and low sunlight in many areas), make it difficult for many species of plants to take root.
As a result, several of the more successful plants in the region are ones that had evolved to draw their sustenance from the delicious flesh of insects, and other things (cough, ahem) larger than insects. Birds, perhaps. A rat or two. Maybe, I don’t know, a human sometimes? Who’s counting, really?
Sticky tendrils, grasping appendages, alluring lights, digestive juices: the flora of the Valley have a wide range of adaptations for ensnaring and devouring hapless fauna.
Several of the plants, like the melaine mushroom, have useful medicinal applications, provided one can harvest them without being eaten.
There’s a decent amount of seismic activity in the Valley. Pocalo is generally highly resistant to earthquakes, as the construction-grade cloud spider silk is slightly flexible and highly shock-absorbent. But a particularly severe quake with just the right combination of vibration and shear forces got the better of Pocalo, and the next day people had to wonder, “Where did that giant rift come from?”
The Rift stretches for several miles across the Muru interior, and plunges several hundred feet down into Eradu, the province immediately below Muru.
This major geographic change also altered the course of the Red Silt River, forming a lake known as The Flood, which drains into Eradu in the form of a huge waterfall. During dry times this can cause the river to stop flowing further south from The Flood, causing water management problems for folks downstream.
Both The Rift and The Flood have made any form of travel across Muru a bit of a challenge. Boats can no longer ply the course of the Red Silt River. And the one crossing point, the Cashel Bridge, is in the process of sloughing off into the Rift.
Because The Rift appeared overnight, the Cashel Bridge was put up in extreme haste, with the idea that a better, more permanent solution would be implemented later. After only a few years it has begun to fall apart, but there’s little incentive to build a more permanent crossing. Most people have opted for more reliable alternatives, and have abandoned the pre-Rift routes that took them past this region.
The eponymous Silk Sky in the Valley is a multi-leveled, mostly-opaque structure made of the silk of domesticated cloud spiders (“Pocalo” literally means “spider web”). So how does light get down to the interior of the lower levels? The answer: LIGHT HOLES.
Throughout each province you’ll find numerous holes in the floor and in the ceiling, which allow sunlight and rainwater to filter through. Not too surprisingly, the further down you go, the less light and rainwater you get.
In general, for the lower provinces, populations cluster at the edges where the light is present throughout the day. An interior area that gets particularly good daylight coverage is called an oasis, and may have sufficient resources to support a small settlement or a waystation. Even if they aren’t suitable for permanent habitation, they’re usually an excellent source of rare plants, or can make for decent temporary campgrounds.
The Red Cities predate the giant web structure that houses the current provinces of Pocalo, but the people of the Red Cities were the ones who developed the technology to use cloud spider silk as a building material.
The earliest structures in the Red Cities were carved directly out of the mountainside rock. When the people needed to expand or repair the buildings, they initially used the cloud spider silk as a base for concrete or cement, mixing it with dust and gravel leftover from carving.
Later technological developments (domesticating and breeding the cloud spiders for different types and consistencies of silk) allowed them to build without the use of stone at all, thereby reducing the weight of the structures considerably.
The Valley is prone to earthquakes, so solid stone buildings are very susceptible to damage, whereas the flexibility of the web structures make them highly resistant to earthquakes.
The Red Cities were largely abandoned during the War of Light. Some have since been reclaimed (by bandit groups more often than not), while others were left to crumble. Although the Red Cities (both active and ruined) are technically governed by the laws of Pocalo, very few resources are actually spent enforcing those laws, giving the Red Cities a reputation as dangerous places to frequent.