Fallout Shelter random encounters

Dwellers sent to explore the wasteland may find locations to explore as random encounters. When they do find a location, an icon appears in the upper-left corner of the screen. Tapping it allows the player to order the dweller to explore or ignore the location. Exploring it opens a side-exploration area where the player directly commands the dweller, and a quest objective in exploring the area is given.

Random encounters will only trigger once the Overseer's office is built.