A single moon orbits the planet.
The major settings of Warbreaker are T'Telir, the capital city of Hallandren, and Hallendren's bordering mountain state of Idris. The jungles are situated in a large valley surrounded by mountains and a sea.
Not much is known about the geography of Nalthis. There is an inland sea that is valuable for trade, and at least a third of the coast is owned by Hallendren.
Hallendren is unique in the known world of Nalthis as being the only place that Tears of Edgli will grow, as well as being the only jungle climate.
Idris is located to the north of Hallendren, the mountains being very profitable for trade, so it can be inferred that a few well-populated nations are located past these mountains and beyond the reach of the inland sea. Idris also contains some copper mines.
Nalthian history is mostly unknown. At some point Vo travels over the sea and becomes Returned, creating the Hallandren nation which occupied the location of the previous Pahn Kahl nation. The Returned create a religion and nation surrounding their abilities. After some time, the Five Scholars come together and participate in the Manywar, which results in the separation of the Idrian nation (after the royal family deserts Hallendren for Idris, for disputed reasons) and the rise of the God Kings and absolutism of the Iridescent Tones. About 300 years later, during the time frame of the book Warbreaker, the Pahn Kahl rebellion occurs.
The Shard Endowment has been confirmed to be present on Nalthis. This has had the effect that any human born on Nalthis is born with one Breath, the source of energy for Awakening and Returning. Endowment has also been said to be related to the dyes which grow around T'Telir, the capital city of Hallandren. Endowment has also been known to return some recently deceased people back to life, awarding them a single Divine Breath under the requirement that they consume a normal breath once a week to stay alive. It is believed, and confirmed for at least three characters, that all Returned come back to fulfill some divine goal. It is unknown what Endowment's purpose is, or how long the shard has been doing this. Warbreaker accounts for only a brief history, which mentions Vo as being the "first returned", as it is said in the Idris religion.