What is burrow space?
Although in relation to our 4-D space, burrow space is almost infinitely small, within its own boundaries it stretches infinitely in three dimensions of its own.
Burrow space is infinite and largely empty. However, the burrow stuff that seeps in through natural doors serves to create a nearly impenetrable mist. In some places the mist has condensed into streamers or branches. This usually indicates a high-traffic area. These clouds are very dense, resulting in zero visibility.
There are places within burrow space where bases have been established. These bases are in general research stations set up near unexplained or unusual phenomena so they can be more easily studied. However, there are exceptions to this rule. The "forward bases" are combat fortresses hovering in burrow space. Located near natural doorways, they serve to keep hostiles in their own dimensions or at least to deny the native Breacher access to a natural doorway in their home realm. This type of action is called a "blockade."
The most famous of the forward bases is Deep Burrow 5. This base blockades one of the most active and dangerous of Breacher realities, the Stikquito home realm. It is believed that the initial Stikquito breakout occurred through this very doorway.
Deep Burrow 5 maintains a cadre of veteran hamaestar, dedicated to the maintenance of the station and the containment of the Stikquito slaver menace. Under their watchful eyes, there have been no major outbreaks. Still, a few Stikquito manage to escape with each attempt. These then join with small enclaves of Stikquito in other less heavily policed dimensions. There they breed and multiply, hoping one day to free the vast numbers still locked within their home dimension.
Of greater interest to historians is the research station Rupert/Wooly. The Rupert/Wooly is located near the ruins of a once powerful species, the Trall. The Trall moved from their terrestrial dimension to live entirely in burrow space. They established stations throughout burrow space near phenomena and dimensions they wished to study, but these were small compared to the vast ruin that served as their capital. The capital is a marvel of burrow space engineering that has survived countless burrow storms. As yet, no trace of a living Trall has been found. They left extensive writings which have defied Hedge Wizard and Mathematician efforts to translate them. Most of the species they studied maintain some form of "visitor" legend regarding them. Otherwise, not much is known. Even the various legends of those they visited do not contain any corroborating information on what they looked like, leading some to speculate that, perhaps, they were a metamorphic species.
Strangely, no mention is made of them in Earth legends, but it is quite clear they maintained several bases near natural doorways to Earth.