The Garden of Shade and Shadows

From the introduction: Two millennia ago, the Valeran elves crafted arborstones, magical relics able to instantly create wondrous gardens (much like a magnificent mansion spell). These were symbols of status and pride, but many fell to corruption when the elves retreated and the shadow fey appeared. The elves who stayed behind did their best to hide or destroy any remaining arborstones, but a few slipped through their grasp.