How high up do I need to be to see across Lake Michigan? (apps.chicagotribune.com)

Ha! I created this years ago. It's just an approximation.

https://gabrielsroka.github.io/webpages/distance.htm

If you're lucky, not very tall at all, thanks to atmospheric bending of light

Here's an example I found on flickr:

https://flic.kr/p/swQrVy