It consists of hundreds of twisting, turning tunnels and caverns, some of which surface in our world, while others surface in other Fears' domains. Distance within a Hive is usually distorted heavily, causing every mile walked through the tunnels to become many miles or only a few feet when an individual surfaces. Most, but not all, Hives are located in a similar unknown universe where they tunnel through living flesh. Some speculate that this may be some sort of micro-universe and the flesh is that of a current victim infested by The Intrusion. Inside the Hive one will find an environment suited to the particular arthropods found there. Hot and dry for insects found in a desert environment, warm and moist for jungle or wetland bugs, and so on. Some areas may even have submerged sections for aquatic arthropods. The Hives also contain arthropods not seen in our world either because they're currently thought to be extinct or because they're something new that developed in the tunnels.
Accidental entry is sometimes achieved by exploring the tunnels or caves that a particular Hive is linked to. In other cases people simply have bad luck and step into something similar to a trap like those made by Ant-lion larva. Some characters describe it feeling like the world was crumbling away beneath your feet until they slip down into the Hive. These traps are commonly found in rural areas, but some have been encountered in cities.
Usually people are brought to The Hive so their bodies can be used as "cocoons" for larvae, to be converted into a Drone, or simply for food. Drones perform much of the manual labor within the Hive, digging the tunnels and such. Specialized Drones are sometimes sent out to bring back things or people to the Hive or to combat threats.