An ancient Vaal treasure temple named is PoE trade currency focused completely on by incursion. "The central core of Incursion is that activities you make in the past can impact the present day," Chris Wilson, lead writer at developer Grinding Gear Games tells me. No one knows where to locate it, however a character called Alva Valai includes about the best way best to uncover its location a hypothesis. They'll encounter Alva, as players enter each new area during a effort. She will offer to utilize these stones to ship one as it existed previously if you talk to her. In doing so, you show the location of this temple because it exists in the present.
All these incursions send you into a random area within Atzoatl previously at which you'll just have a limited period of time to kill all of the critters found there. Each kill grants you more time, but you are still going to need to move. A pub on the bottom of the display tracks your progress toward killing every creature in the area and, once the timer runs out and you are sent back into the present, all the items you would have gathered cheap poe currency spill out in one glorious fountain of loot.
Wilson tells me that this is the first layer of Incursion: Here's a room full of monsters to kill and a fountain of loot to enjoy for doing this. It's something that breaks the stream of the campaign.