Assuming you own an OKM detector (or have demo files to view), follow this guide:
From a top-down view, the "anomaly" wasn't a random shape. It was a symbol. A perfect geometric symbol carved into the earth—a circle with three intersecting lines. It was precise. Too precise for 1920s construction. okm visualizer 3d for android free download
Find the for your specific detector model. OKM Visualizer 3D: A Powerful Metal Detector App
Once you have installed the legitimate free version, here is what you can expect: here is what you can expect: