The Elemental Plane of Fire
The Tower of Grey, on their mission to save the world, visited Ioun, goddess of knowledge, seeking information on The Orb, which was showing them images of location throughout The Multiverse. One of those locations was The City of Brass, within The Elemental Plane of Fire.
They finally ended up traveling there in Episode 334, and, as expected, it was very hot. There were flames and volcanoes everywhere. The party were attacked by some Efreeti guards, who they beat and made take them back to the city.