Terrain Simulator

When practicing for marathons, runners often spend upwards of three hours on a treadmill. This gets very boring. I'm proposing a large screen fixed to the front of a treadmill that would show videos of appropriate terrain matched to the speed at which you walk/jog/run.

Users would be able to buy/download additional "routes", such as famous marathon courses, or city-scapes, or country-scapes. They might even be able to select alternate routes at some points along the course. The machine should adjust elevation to match the video. The program could even insert other runners to add a competitive element to the simulation.

I considered VR glasses, but they seemed dangerous due to not being able to easily see the belt under your feet, and the extra weight would be a deterrent to many serious runners.

I've done some searching to see if this has been done before, and didn't see anything right off the bat, but really all I wanted to do is get the idea out from my POV. Comments very welcome!