This achievement requires the player to be the Hexoatl faction and build the Vaults of the Old Ones in the city of Itza. It be gained in both the Eye of the Vortex campaign and the Mortal Empires campaign.
I've researched this achievement online and it seems the Last Defenders faction (also Lizarmen) cannot build this building in Itza, only Hexoatl can.
Itza is part of the Southern Great Jungle in Mortal Empires and the Northern Great Jungle in Eye of the Vortex. In both campaigns the city is occupied by the Itza faction.
Conquer the city with an army or confederate the Itza faction. Upgrade the city to lvl 5 and build the Vaults of the Old Ones. After the city is build, the achievement should unlock.