Ever year, Matt Parker calculates pi, and this year it was the largest manual effort to calculate pi in a very long time[1] . I took part this year, though I didn't end up in the video sadly. It was lots of fun though, and a nice trip to london
I put together an iPhone app that guides you through all the steps needed to compute Pi to 100 decimal places. Surprisingly enough, this doesn't require any complex math -- just basic addition, subtraction, multiplication and long division. The hardest part is verifying your intermediate results, and the app will do that for you. In testing it, I've been able to compute about 40 digits by hand. The way I look at it, some people climb mountains, and others run marathons... I figured it'd be an interesting challenge to see if I could calculate Pi by hand.
[1] https://youtu.be/LIg-6glbLkU