Sigil and the doorway to nowhere
The City of Clairemont is one of the oldest Dwarven fastnesses, and one of the largest. The city itself is almost entirely underground with humans and halfling hamlets, and farms covering the slopes. When Woskgaw’s trade routes fell to slavers and raiding became a problem the dwarves used the natural lay of the land, and detritus from mining out the city, to form a wall cutting off the outside world.
Now it is almost impossible to get into the city. Leaving the city is even less likely, as most have no intention of leaving the safety thereof. Almost everything the city neededs can be built within it or grown on top of it.