A horde of devious, ferocious, tenacious, and atrocious creatures, beasts, and monstrosities to populate the northern realms of your fantasy. Get them while they're cold!
You come upon a ruined building in the back section of a city park (or other out of the way area of the city). The ruins are fairly overgrown. All that is really standing is a doorway and its frame. If you pass through the opened door, you travel to a different world. If the door closes, there may not be a doorway back to get you back.