Beacons are a possible objectives found in the Monolith of Fate.
Mechanics
Beacons are large stationary crystals that can be randomly found in normal Echoes. A beacon can be located and lit in order to reveal additional Echoes beyond the usual sight range on the Echo Web.
When in a mission, the Beacon's location is visible. Once reached and stepping in its circle, the Beacon will start charging, while also attracting numerous Void monsters. The Beacon will keep charging as long as the player remains in the circle; killing monsters simply removes their threat.
Once the Beacon is fully charged, the Void entities instantly perish and the Echo is completed, allowing to portal out.