The Black Web - 796th Layer of the Abyss

In the abyss are many layers that never see any sky, and this entirely subterranean cave complex is one of them. It is made of an infinite number of bubble-like caverns carved entirely unnaturally out of the black rock, some as wide as a head and others large enough to hold a city. Stretched out over every surface and between every point of prominence are thick bundles of webbing that span into the darkness. Additionally, coating every single surface, dripping down silently and endlessly from some unknowable source in the ceiling of each cave, is a black ichor more poisonous than any toxin ever known. Finally, the entire plane is entirely without air. A nearly perfect vacuum, it boils water from the skin of creatures entering from wet environments (such as Black Bile Cove), and creatures that need to breathe will die in moments.
In the larger caverns, the webbing forms large knots at the heart which are hundreds and sometimes thousands of feet across. These tangles are where Viskardis, the Queen Retriever, Jailer of the Undercourts, and Prince of the 796th Layer, lays pearl-like eggs that serve as jail cells for those creatures and souls the most powerful Demons wish to preserve. They protect the creatures inside them from the vacuum and poisons of the layer, suspending them in time until the Demon Lords negotiate with Viskardis again for their release. The Queen Retriever often sends her construct familiars out with her eggs to retrieve prisoners as they arrive, and directs their storage.
As Viskardis herself is described as a retriever monstrosity with individual legs hundreds of feet long, it is unlikely to encounter her in all of this realm's caverns, but her presence and keen intellect can be felt in the eyes of all of the retrievers that pay her heed.