The Moon Gate comes with the special set bonus. When it is adjacent to other buildings belonging to the Celtic Forest Set the properties of the building are improved.
The Moon Gate can be upgraded by Moon Gate Upgrade Kit item. To upgrade the Moon Gate, use the Moon Gate Upgrade item on the Moon Gate that is already situated in your city. Its upgraded version will then be placed directly on the same spot in your city and the production timer will not be reset. Note that the upgraded building will be from your current era, even if the old one was from one of the earlier ages.
Moon Gate will produce the following effects. Base effects will always be produced. Bonus effects are determined by how many other unique Celtic Forest Set buildings it is connected to.