The Renovation Kit
Upgrades special buildings from a previous age to the current age.
The Renovation Kit can be used by its owner to upgrade a special building acquired in an earlier age to the player's current age. Each kit can only be used once.
A player owns for example a Shrine of Knowledge obtained during the iron age (and of course a renovation kit). The player later finds out (for example during the modern era) that he or she wants to upgrade it to the player's current age. The player then picks the renovation kit placed in the inventory and clicks the Shrine of Knowledge of interest (a star is highlighted above upgradable buildings) and confirms the upgrade. After confirmation the building has the properties of the current age rather than the properties of the age during when it was obtained. The renovation kit is then consumed and removed from the game.