Amazon is offering all three BioShock games for Windows PC as a $19.99 bundle, down from the full price of $99.99.

Irrational Games' first BioShock, set in the broken underwater city of Rapture, was released in 2007 to universal praise, carrying a Metacritic score of 96 percent. The first-person exploration and shooting game investigated issues like utopian Objectivism, while tasking players with challenging moral choices. A sequel, 2010's BioShock 2, was developed by 2K Marin.

Earlier this year, Irrational and publisher 2K Games released BioShock Infinite, which Polygon scored a perfect ten, calling it "a believable, fantastic world rooted in dark pieces of American history."

Amazon's offer is download-only and runs through Sept. 25.