Experience

Overview
The player gains EXP by completing building projects and tasks in order to increase their city level. Each level increases the maximum number of buildings allowed in the city, and unlocks new projects. The last building is unlocked at level 70.

You gain one Golden Key with each level up, and 2 Keys every 5 levels. Current EXP, level and buildings cap are shown in the "Your City" menu. The game loading screen also displays level and days played on the bottom. Building and upgrading a University will boost experience gain. Also, at the start of the game, some (which?) level ups will fill the energy bar to full.