The Sea of Tranquility, or the Mare Tranquillitatis, is located on the moon. Although the feature at first appears to be a body of water, the Sea of Tranquility does not actually contain any water.

The Sea of Tranquility is a flat, dark plain on the moon called a mare. It was the place that was chosen to be the landing site for the first lunar landing. Whereas much of the moon features craters formed by bombardment by objects during the moon's history, the mare regions are almost completely void of craters. The maria were formed by the oozing up and spreading of molten material from within the moon through cracks on the moon's surface.