One thing I miss about G+ is how you could just quickly post a couple of ideas and leave them hanging there for later consideration. Doing so on a blog like this is not as easy or as simple, but still is a lot better than scribbling out an easily-lost note.
One thing that has struck me recently is dungeons -- a lot has gone into discussing why dungeons exist in such ubiquity in fantasy game worlds, other than the obvious need for adventurers to go into them, raid the monster lairs within, and bring out treasures. One obvious reason, of course, is that there are actual subterranean races in the world, so naturally, they are going to want someplace to live, and unlike the surface races, who built out and up when they left the caves, the subterranean races built in and down. Another major reason discussed is for safety against large monsters, such as dragons and giants; stone buildings just won't cut it, so dungeons are more common as being easily defensible.
|You can't tell me the walls inside aren't enchanted...|
Another reason is for defense against magic. Lots of magic spells are inoperative through more than so much metal or a larger stretch of stone, so a home deep within the rock of the earth is going to be nicely defensible against such spells. Add to this the ability to enhance that defense in all three dimensions and dungeons look even more appealing. You can't cover an entire surface city in lead or three feet of rock but if you build your city underground, the entire thing is immune to certain spells... and if you put defensive runes on the ceiling, you have even more defense against magic. If you build out the walls, you have even stronger magic built in to the defenses (why are there dressed walls everywhere in dungeons? Simple... to put magic in the walls, which is even stronger than runes alone).
Of course, there is no system for such kinds of defensive magic at all in the game; but then, there is also no system of magic in the system for clerics of agriculture or druids to enhance harvests and such, yet it is kind of assumed that they do. So that's a system of magic that might need be detailed for long-term campaign play...