Cahokia Mounds

The largest pre-Columbian city north of Mexico, Cahokia was home to over 20,000 people at its peak around 1100 CE and features 80 surviving earthen mounds, including the 100-foot Monk's Mound — the largest prehistoric earthwork in the Western Hemisphere. The city was mysteriously abandoned by 1400 CE with no definitive explanation. Visitors report an eerie silence even during crowded tourist days, compass disturbances near the central mounds, and a persistent feeling of being observed. Researchers have detected anomalous geomagnetic readings beneath several of the smaller satellite mounds.