Ritual Altar

Ritual altars show up in groups of 2 or 3 on maps. They are inactive until enough enemies are killed within the radius of the altar to active it, and gradual light up per kill until fully activated.

The first ritual altar on a map will re-summon the enemies killed within the radius, and give you tribute.

The successive ritual altars will do the same, but will also once again summon the enemies that were killed within the radius, which means you can kill the same rares/uniques multiple times in the same map if they killed within the radius of the altar.