Braavos

Founded in secret by escaped slaves in a fog-bound lagoon, and now the richest city in the world.

The fuller tale

It is the youngest of the Free Cities and the only one Valyria did not build. A fleet of slaves ÔÇö of a hundred tongues and a hundred gods ÔÇö took their masters' ships and hid in a lagoon behind a wall of pine-clad islands, and stayed hidden for over a century before announcing themselves. The day they did is still kept as the Uncloaking.

Everything about the city follows from that beginning. Slavery is the one unforgivable crime; every faith has its temple on the Isle of the Gods; and the Iron Bank, which is what happens when people with no land and no farms decide that money is the thing to be very good at, holds paper on half the crowns of the world. Its motto on that subject is not a threat so much as an actuarial statement.

It also keeps a temple to the god that everyone eventually meets, staffed by people who are extremely good at arranging the introduction.

The ground they held

 See the world in 298 AC on the timeline 

What became of it ÔÇö if an ending is written, it is here. Spoilers.

The chronicle records no ending here ÔÇö or none the maesters have set down.