Indoor Farms are food production buildings, meaning they only produce food for your citizens to harvest and later eat. They are the 3rd 'Production' building you unlock.
Usefulness of Indoor Farms[]
Indoor Farms are very useful in making food, especially when buffed by other buildings. Indoor Farms can be buffed by Labs to Increase the amount of food you receive every harvest (7) and an Experimental Farm to slightly increase (by how much) the growth rate of crops in Indoor Farms. Indoor Farms are also one of the cheapest buildings in the game, allowing you to easily build them while barely losing any resources.
Farming cave paintings increase the about of food per harvest by 5. Therefore, the highest about of food you get per harvest is 25 + 5 + 7*4 = 58.