Quote Originally Posted by Bohandas View Post
That would be massively expensive under D&D rules though. That's like an 11200 gp device for everyone. A really really lenient DM might let it be done with a single 56,000 gp device (if we let the magnificent mansion spell be cast at way way below it's minimum caster level and rule that it leads to multiple different places while still in effect; instead of more doors to the first one until the first one is dismissed) but even then it could only serve 14400 people because it takes a round to use it.
Nonsense! Kill an Ancient Red Dragon or two and you'll have more than enough. Clearly the town was founded by a retired Adventurer; boredom provided the inspiration and his Epic WBL took care of the rest.

Or a God, or an extinct Elder Race did it, or something. DM fiat should likely be in charge of any city-sized construction to be honest, there average player probably shouldn't reach that sort of level of power.
To use the same example as before; Sigil exists as a template so we have proof that it *can* be done, and we're just building something similar that happens to be finite in size instead of otherwise.