During the International Baccalaureate Higher Level Mathematics program, a required component is the Internal Assessment, a written report which explores a real-world application of math. For my IA, I calculated the volume of an onion dome atop St. Basil's Cathedral.
I did this by applying the proportions of the image of the dome on my screen to the real height of the cathedral in order to calculate the dimensions of the dome. I then modeled the dome using an ellipse and cotangent function, applied constraints, and solved for the volume using integral calculus.