That's useful, thanks. But to be a bit pedantic, this can only show that at a particular place where the measurement is taken, the earth has some curvature, that its a bit like a hill there. This does not show that the earth is globally a sphere, which would mean for example that if you go in the same "direction" long enough, you arrive at the same point.

Sure. But the game is to think of experiences that are more or less likely depending on which guess is true. Any ‘crucial’ experiment is only so given some background.

It might be fun/useful to spend five minutes writing down all the experiences like that that you can think of. (E.g. I’m writing this from a town on the edge often Rocky Mountains facing a plain. If I climb up, how would how far I can see vary with the height?)

"This video contains content from eOne UGC, who has blocked it in your country on copyright grounds."

It’s a clip from Carl Sagan’s “Cosmos: A Personal Voyage”[1]. Searching for “Eratosthenes” returns tons of other videos that explain the experiment.

[1]: https://en.wikipedia.org/wiki/Cosmos:_A_Personal_Voyage