Europe's Oldest Human-Made 'Megastructure' Discovered under Baltic Sea

Archaeologists have discovered what may be Europe’s oldest human-made megastructure, submerged below the Baltic Sea and dubbed the Blinkerwall

https://www.scientificamerican.com/article/europe-rsquo-s-oldest-human-made-lsquo-megastructure-rsquo-discovered-under-baltic-sea/