Opening holes in reality may seem like a good idea when an Ice Age is quickly devouring peoples’ lands, but when a Gate goes wrong, things come through. Faeries, undead, demons all come crawling through to stake their claim on this ancient land.
Aebryn has finally entered a time of peace, the Dwarf King Oedan has brought the warring nations under his control and has ushered in a new time of enlightenment and progress. The use of Gate magic is outlawed, but too late; the realm is under siege from a bizarre universe, the Dungeon realm. Deep and filled with a nonsensical ecosystem, Living Dungeons rupture through to the surface, spilling hordes of monsters.
After that, take a look at your wiki. There is some more helpful info there.