This is a simple app that calculates the distance to the horizon from the height of your location.

Intuitively, a person would expect that curvature of the Earth is unnoticeable in everyday life. However, it is interesting to note that after you had a walk of 5 km straight, your path actually also went "down" 2 metres because of the roundness of the planet. This can also be seen while watching distant boats using binoculars where you might notice that their bottom is "missing" below the horizon. It is well known that ancient Greek scholar Eratosthenes calculated the circumference of the Earth almost correctly based on similar curvature observations alone.