City of Brass

The hottest city in the multiverse.

The City of Brass is a location in Arabian mythology. There it is an abandoned ruin in some desert, usually North African, filled with traps against would-be pillagers... like the protagonist of the story.

In Dungeons & Dragons

Jeff Grubb in Manual of the Planes set the City on The Plane of Fire - for what we now call the Great Wheel. It's in a forty-mile diameter bubble. It is the capital-city of the efreeti, a race of fire-aligned genies. This is often a place where adventurers will go to find magic items, because... well, efreetis. Likewise, it's a hub for interplanar trade.

The World Axis sets it in the Elemental Chaos.

Canonically some human archmage took this city: Tzunk. Talk about a mad lad. This is attributed to Tzunk's then-ownership of the Codex of Infinite Planes. (It is assumed Tzunk was unable to keep the city.)

Unusually for a planar location, which Wizards normally guarded with jealous attention, this instance of City of Brass also exists in Pathfinder, and also on its Plane of Fire. This is likely due to a stray reference in the text for Unearthed Arcana and to the "Codex" entry in the Epic Level Handbook, both released under the Open Gaming License. The former mentions a visit to "the City of Brass where they must bargain with an efreeti lord". As for the latter, it notes that the Codex has passed through its "fires".

In Pathfinder

In the Pathfinder setting, the City of Brass featured prominently in the Legacy of Fire adventure path, where the PCs are trapped in an enemy fortress within the city and are tasked with recovering an artifact known as the Impossible Eye. A unique feature is that the foundations of the city are living brass, a metal created from the souls of mortals who made terribly-worded Wishes. The city is ruled by a tyrannical grand sultan, but his vizier holds just as much power unofficially and the two spent lifetimes scheming to upend each other.

In Al-Qadim

Secrets of the Lamp was the genie-centric sourcebook for Al-Qadim, and as such it detailed the city along with an adventure set within. It is much more martial in nature, where districts are set up as military zones and colonies are maintained all around the Elemental Plane of Fire.

In the Lost Lands (Frog God Games)

The City of Brass in Frog God Games' (at the time, Necromancer Games) Lost Lands Setting has more overtly Islamic and Arabian backstory, where the city was originally a multi-cultural creation for the gods' children but the efreeti wanted it for themselves. They were cursed by Sulemein for this transgression, and the Grand Sultan seeks to avenge this dishonor and claim the legacy of godhood. Is notable in that the city is not in the Elemental Plane of Fire, but rather in a demiplane of its own sitting at a crossroads between the non-water Elemental Planes. Originally available for 3rd Edition D&D, a KickStarter updated the book for 5th Edition and Swords & Wizardry along with a full level 1-20 adventure path.