https://www.metabunk.org/threads/soundly-proving-the-curvature-of-the-earth-at-lake-pontchartrain.8939/
A classic experiment to demonstrate the curvature of a body of water is to place markers (like flags) a fixed distance above the water in a straight line, and then view them along that line in a telescope. If the water surface is flat, then the markers will appear also in a straight line. If the surface of the water is curved (as it is here on Earth) then the markers in the middle will appear higher than the markers at the ends. Here's a highly exaggerated diagram of the effect by Alfred Russel Wallace in 1870:
This is a difficult experiment to do as you need a few miles for the curvature to be apparent. You also need the markers to be quite high above the surface of the water, as temperature differences between the water and the air tend to create significant refraction effects close to the water.
However, YouTuber Soundly has found a spot where there's a very long line of markers permanently fixed at constant heights above the water line, clearly demonstrating the curve. It's a line of power transmission towers at Lake Pontchartrain, near New Orleans, Louisiana.
The line of power lines is straight, and they are all the same size, and the same height above the water. They are also very tall and form a straight line nearly 16 miles long. Far better than any experiment one could set up on a canal or a lake. You just need to get into a position where you can see along the line of towers, and then use a powerful zoom lens to look along the line to make any curve apparent.
One can see quite clearly in the video and photos that there's a curve. Soundly has gone to great lengths to provide multiple videos and photos of the curve from multiple perspectives. They all show the same thing: a curve.
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Flerfers also do this thing where they wave left to right, or even 360 degrees all the way around and say, "wHeRe'S tHe cUrVe?" Right in front of you.
You're standing on a ball. Looking around laterally is seeing the points of a cross-section.
The curve is away from you, not around you.
