(Sparkypants Studios) When I read the short story Tower of Babylon by Ted Chiang I was inspired to model a tower of my own. In his story he described people living on the tower spending their entire lives ferrying food, bricks, and mortar up to the next level where it is passed along. This sparked the idea of a game where the player would gather resources and combine them into materials to race upward toward the heavens constructing their own tower. To add challenge we put in "enemies". Bugs and plagues that would slow or stop the player's progress. At the beginning it was just me concepting and building. Then I was joined by Pranas who coded everything and made it a playable game. Then the game gained some traction, more people jumped on the project and morphed into a tower defense on a tower.
This video shows the unity proto in a state where bugs attack from below and fly down to the base to destroy the tower. The enemy turrets on the tower are how the player defends their construction.