Oldie, but a goodie. Come spend a couple minutes with Carl Sagan as he explains how Eratosthenes figured out the circumference of the earth and that it truly was a sphere!
The pacing is a little slower than we're used to these days, but it's a relaxing five or so minutes. Rebel against the attention economy for a moment this Friday and indulge yourself.
Oh! Final bit of fun info:
Eratosthenes was measuring the circumference north to south, not around the equator, because that's the orientation of the two cities he used. He was actually only off in his calculation by ~7.86 kilometers (that's ~4.89 miles for our Amerikan friends). Amazing!