Shadow realms get a lot of use in mage society. There’s a lot of things you can do with a pocket world, and over the millennia mages have come up with some very creative uses for them. Here’s a brief look at some of the more common ones.
Magical research is slow, difficult, and often dangerous. If a mage is trying to adapt a spell, develop a new ritual, or work on a magic item, it helps a lot to have a quiet, out-of-the-way location to do it in. It’s always possible to find a sparsely populated area on Earth, but with the number of people in the modern world, finding a really deserted spot is harder than you’d think. The more destructive and dangerous the process, the more deserted the place needs to be – you can make one-shots in your garage or bedroom, but if you’re practising inferno spells you want a REALLY big firing range.
For this purpose, shadow realms are perfect. They’re as quiet and deserted as you’re going to get, and the chance of random normals wandering in while you’re in the middle of something is practically zero. If a research-oriented mage doesn’t want or can’t afford a mansion in the middle of nowhere, their first priority will probably be to get access to a shadow realm instead.
Training apprentices has all of the problems associated with magical research, only worse. With research, a mage can at least assume that the materials in his workshop aren’t going to spontaneously explode on their own. If he’s training apprentices, it’s more or less a guarantee that sooner or later they’ll do something incredibly stupid. In these situations it’s very handy to have a place to hold lessons in where bright lights, strange noises, things catching fire, explosions, monster summonings, and holes in reality aren’t likely to draw attention or endanger passers-by. Whether the shadow realm is going to be in particularly good condition afterwards is another matter.
Some mages who’ve found a shadow realm to their liking decide to cut out the middle-man and move in. They pack up their bags and emigrate all the way out of our reality.
Shadow realms have definite selling points as residences. You don’t have to worry about paying rent, and you can ignore those annoying zoning ordinances and property taxes too. Spam mail’s no longer a problem and you rarely get visitors you don’t want. On the other hand, mages who try to make a go of living in a shadow realm quickly discover the drawbacks (covered in the next entry). Some mages stick with it and find workarounds, but they’re a definite minority – most eventually find that for all its problems, Earth works better.
Shadow realms are very, very good when it comes to natural security. The only known way to reliably reach one is via gate magic, and even then you generally need either to have been there or to have a focus to provide a link. What this means is that for somebody else to reach your shadow realm, they have to first have access to gate magic (which rules out well over 99% of the population), then know that your shadow realm even exists (which rules out well over 99% of those that are left) and finally have the links and skill to pull off a gate spell to get there (which rules out an indeterminate amount of those remaining, quite possibly 100%). All in all, the most likely way someone’s getting into your shadow realm is if you invite them in.
That said, every security system has a weak spot, and mages are nothing if not resourceful. Given enough time and motivation, mages can figure out a way into even a shadow realm. If you want your shadow realm to be truly secure, it’s wise to have additional layers of defences beyond the natural ones.
For all their wonder, shadow realms can be put to darker uses. While most mages don’t discuss it, it’s common knowledge that many mages – notably, but not exclusively, Dark ones – employ their shadow realms for purposes of imprisonment, interrogation, and worse. To anyone incapable of gate magic, such prisons are virtually inescapable. Some rare shadow realms are even designed as prisons, and they’re truly hellish.