The Nuclear Shelter
The Nuclear Shelter is one of the five Modern Era decorations and can be build after researching Mechanized Artillery. When the Nuclear Shelter is polished, its output of happiness is doubled for 12 hours. Decoration does not need a road connection. On the main doors are the letters inscribed 101. This could be of reference to the Fallout game series where underground vaults are used as nuclear shelters in a retro futuristic world. In the game, Vault 101 is where the main character grows up.
+68.75 per tile.
Your decoration can be polished to double the happiness provided to +550 for 12 hours.