Io in Destiny 2.

Io is the largest moon of Jupiter. It was one of the last places that the Light of the Traveler touched during the Golden Age. This makes Io a very significant place within the mythology of the Traveler and very important to Warlocks. The Traveler calmed the intense volcanic activity native to the moon which allowed it to be terraformed.

Warlocks will often make a pilgrimage to Io to honor the Traveler or when they seek very deep answers. Ikora Rey is said to have done this.