All you need is a yardstick and a friend with another at a different latitude so you can measure at the same time (using an accurate clock or a video call). Alternatively, you could test in two locations at different times at local noon in each longitude (even works if you spread the measurements across years, as long as your dates are fairly comparable).

The ancients had an estimate (accuracy notwithstanding) for the diameter of the earth. It's not hard to suss out.

I agree that enough sources is close to actual proof. How is it that USA, China, North Korea and Elon Musk are all flying to space, yet never even hinting that they "know" the Earth is actually flat? So, not only the evidence provided by those who know, but also the lack of evidence to the contrary from individuals and groups that are often more like enemies than co-conspirators.

But there is an Earthbound layman way to witness it for yourself, with your own eyes. For me, here in Toronto, I just have to go around Lake Ontario to Niagara Falls, and then look back across the lake toward the CN Tower.

You will see no sign of Toronto Island, nor the Skydome, nor the majority of midrises. But they are in fact, there. You know this because you saw them just 45 minutes before you arrived to Niagara Falls for this experiment.

A lot of it is just below the horizon: You can see about 1/2 of the CN Tower's height, and a good handful of the highrises, so you know it's not an illusion.

For that matter, from Toronto Island you can only see a couple of Niagara Falls' tallest structures peeking over the horizon. So the observation works both ways, although stronger when looking towards Toronto - Toronto is obviously a much taller city afterall!

How does one explain that without admitting you can literally see that the surface of the water is curved?

So it doesn't take a lot of effort to see Earth's curvature, even with minimal scientific tools. You don't even need binoculars to witness this one. Just a car and 45 minutes of your time.

That's right. Its almost true of any story. But you have a chance of verifying something. Occasionally a story will turn up on your doorstep - you should see if the story checks out with your personal experience.

However, its entirely true of stories in Antarctica. This is because all the nations of the world agreed that they should keep a whole continent pristine - with no one ever allowed free access. Incredible.