From the Ritual of the Blight quest introduced in Shattered Lines.
Located at 38.2S 12.0E in the middle of the A'mun Desert, south of Al-Arqas and northwest of Xarabydun. It is right next to the drop of Fadsahil's Portal Gem (Gharu Mastermage).
The pyramid's light is strengthening, but there will be a long way to go before it is restored. It has not yet reached half strength.
Search for Blighted Sotiris Hollow Minions across the A'mun Desert, they drop Blighted Mana Crystals. Give their trophies to the Node, see A Field Guide to Tainted Nodes for details.