Blinkerwall

I don't think it is shocking that mesolithic peoples built a kilometer-long wall to help them catch reindeer, which we didn't know about because it is now under the ocean, but the simple fact is that I had never heard of it before and now I have.  The Blinkerwall: A Stone-Age Megastructure in the Baltic Sea.  

The hypothesis that the Blinkerwall served as a reindeer trap is supported by its design and location. By herding reindeer towards the lake, the structure likely slowed their movement, making them easier targets for hunting—a strategic advantage that early humans would have capitalized on for survival.