Follow the 1927 airmail route from Indianapolis to Chicago
Before GPS, before VORs, before even radio, airmail pilots navigated by following chains of beacon towers across the countryside. Concrete arrows on the ground pointed to the next beacon. Most are gone, but some survive, hidden in Indiana farm fields after harvest. CAM-24 itself was flown by the Embry-Riddle Company from December 1927, Cincinnati to Chicago by way of Indianapolis in Waco biplanes; its mail operation became one of the seeds of American Airlines.