Shadowcracks are like spiderweb cracks through shadow caused by the Black Road. They are tainted trails along which an ordinary person can travel through shadow, without using a normal shadowpath or the Black Road itself. Travel along such trails is extraordinarily dangerous, as they are essentially a lesser form of the Black Road, but it is possible for characters who have heroic stature (i.e., PCs and those they lead).
A shadowcrack trail, either a land or sea route, leads between a Realm shadow and a Golden Circle shadow. Shadowcracks only exist in this context. If a shadowcrack trail is used in play, the place that it reaches it always significant. Their existence should never be used to circumvent shadow-finding restrictions (i.e., without Pattern, you cannot shadowfind).
Most shadowcrack trails are quite small — they are trails, not roads, so to speak. They may passed unnoticed for a long time unless they are somehow brought to prominence. The endpoints of such a trail are usually unpleasant places, and the trail itself gets more and more unpleasant as one gets away from the endpoints. The trail is physically dangerous; the ground is treacherous and hard travel (or the seas are hazardous, if a sea path). There are monsters in abundance, and the environment itself may be deadly — poisonous bogs, forests on fire, maelstroms at sea, and the like.