The Graveyard is a special cultural building first given as a reward during the 2012 Halloween Event.
The Graveyard provides happiness, and when it is polished, its output of happiness is doubled for 12 hours.
The Graveyard can be upgraded with a Graveyard Upgrade item. To upgrade your Graveyard, use the Graveyard Upgrade item on the Graveyard that is already situated in your city. Its upgraded version will then be placed in your inventory, and the original Graveyard will disappear from your city (note that the upgraded building will be from your current era, even if the old one was from one of the earlier ages).
Graveyards: