Tranquil Garden

The Tranquil Gardens is a Wonder that eliminates displeasure of inhabitants. It is unique meaning you can only have one. It can only be built once you have found all three of the quest's trees, the Tree of Harmony, Tree of Serenity, and Tree of Unity in special ruins which are scattered across the games three regions.

Warning: Tests have shown that this Wonder will not prevent inhabitants from leaving if they are made Angry for too long. More testing is needed to find the limits of this Wonder. Initial test took them to extremes by removing almost all Desire buildings and several houses. Population promptly dropped from 217 (my world's max) to about 147.