… this question was raised by Shadom when he was talking about the importance of being consistent in translations. Apart from Shadom, yennico, Pythia and Dr. Gonzo all try their hand at providing answers for Dresden Files, Iron Kingdoms and generic fantasy.
According to them the dark hollow is:
The dark hollow is a place of power in the Nevernever. It is inhabited by gloomy creatures, once kind and beautiful beings, now transformed into twisted mockeries of their former selves in their hopelessness. They will attack anyone who unlike themselves has not given in to desperation. Directly surrounding the dark hollow are the mountains of light, places of hope and bliss. As near as they may be, they are forever out of reach, for true desperation is only to be found where you realize what can never be yours. If a mortal should ever succeed in negotiating the dark slopes of the hollow, one of the creatures will regain its old identity and will aid its savior until the next sunrise. Passages to the dark hollow can only be created by a ritual and then only when evil triumphs over good.
The dark hollow is a swath of land with dark fertile soil. Here, many farmers cultivate crops, making the area the breadbasket of a kingdom. Only a short distance away, two hostile nations border the kingdom. The dark hollow has always been contested between the three realms and many a bloody battle was fought within. According to rumour, the spilt blood is the reason for the dark color and great fertility of the soil.
For the past decade, there hasn’t been a battle in the dark hollow because the current king is so powerful. It is said that the hollow thirsts for new blood, which it may well get soon enough for the king has fallen ill.
There are also ghost stories surrounding the dark hollow. All farmers set up scarecrows to protect their crops. Those scarecrows are supposed to come alive soon.
The dark hollow is a great swamp filling a deep valley. It is inhabited and guarded by a clan of swamp dragons and thus is nearly free of the influence of men. There are rumours that an ancient city lies sunken in the swamp, its highest spires still rising above the surface. The brave are said to be able to find riches and artifacts beyond imagination there.
The dark hollow is a tavern on Beggar’s Isle. It isn’t dark at all and going by the standards of the isle it is even quite proper and tidy. It is usually frequented by the isle’s more prosperous inhabitants. According to slanderous rumour the tavern got its name from the nether regions of its proprietor, who is infamous for her appetites in both food and men.