Southern Air Temple
The Southern Air Temple is one of four temples around the world where Air Nomads gathered, and the one at which Aang grew up. After he wakes up from his 100-year sleep, he finds the remains of the airbenders there, including his mentor and father figure, Gyatso. Tragically, this confirms that the Fire Nation destroyed the Air Nomads, leaving him the sole survivor.
Northern Water Tribe
The Northern Water Tribe is the largest of the three water tribes, centered in the North Pole. Its capital city is Agna Quel'a, which is carved into the edge of a glacier. Its leader is Chief Arnook. When Team Avatar arrives, they ask the famous Master Pakku to be their waterbending teacher.
Southern Water Tribe
After having been ravaged by the Fire Nation for decades, the Southern Water tribe has nearly gone extinct, with only a few scattered villages remaining. The villages are populated by mostly women and children, since their male warriors have left to fight in the war, including Sokka and Katara's father, Chieftain Hakoda.
Ba Sing Se
Ba Sing Se is the capital of the Earth Kingdom, the largest nation in the Avatar world. It is known for its walls that have protected the city from the Fire Nation's attacks. Team Avatar travels to Ba Sing Se to appeal to the Earth Kingdom's king for support in their fight to end the war.
Omashu
Located in the southwest, Omashu is the Earth Kingdom's second-largest city following Ba Sing Se. Led by the mysterious King Bumi, Omashu has remained one of the Earth Kingdom's last strongholds against the fire nation thanks to its location at the top of a mountain and the guards that protect its borders.
Foggy Swamp
The Foggy Swamp covers much of the Earth Kingdom's southwest region in wetlands dense with trees. It is home to various flora, fauna, and the Foggy Swamp Tribe, who often use waterbending to manipulate large vines and plants. The Swamp is also home to a large number of spirits.
Si Wong Desert
As a large desert in the central Earth Kingdom, Si Wong Desert is famous for being nearly impossible to cross without the aid of the Si Wong Tribes, who survive using sandbending, a subskill of earthbending. Team Avatar is trapped in the desert after Appa is stolen by raiders, but they later reunite with him in Ba Sing Se.
Fire Nation Capital
The Fire Nation Capital is a huge settlement nestled inside a dormant volcano's caldera and is known as one of the world's strongest cities. At its center is the smaller city where the royal palace is located and where many of the Fire Nation's nobility live.
Spirit World
Existing in an alternate plane of reality, the Spirit World often mirrors the primary world and is home to countless spirits. This realm reflects the inner feelings of the Avatar, so when Aang or other characters find their way there, it is spooky and dark to reflect Aang's genocidal trauma.