1. Launch a balloon with your own camera attached to it:
https://www.youtube.com/watch?v=UAifzh7_-cg

2. Sail around the world on your own.

3. Become an astronaut.

...but the curve is going the wrong way in that video!

The options were flat or spherical, now you've gone and complicated things by offering evidence for a concave earth.

With fish eye lens? Of course it is.
I'm surprised "flat earth" theory is still a thing.

Same with evolution,gravity and big bang theories