From the Tainted Ley Line Nodes quest introduced in Shattered Lines.
Located at 93.8N 67.4W on the far northeast side of Traitor's Island, northeast of Silyun. There is a Silyun portal near the drop in Qalaba'r.
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 Hoary Armoredillos across Traitor's Island, they drop Blighted Mana Crystals. Give their trophies to the Node, see A Field Guide to Tainted Nodes for details.