This cache is part of a 1:133,700,000 scale model of the solar system. The dome on the Monroe County Courthouse in downtown Bloomington serves as a model of the sun. Mars is about 6750-6790 kilometers in diameter and ranges from 207 to 249 million km from the sun, so this model is roughly 2 inches in diameter and about 1.16 miles from the Courthouse dome, just at its aphelion (the point in its orbit where it is furthest from the sun).
Mars is the fourth planet from the sun, a rocky world with a slight reddish tint due to the presence of iron oxide on its surface. It's not as red as you might expect it to be because most photos you've seen have been "enhanced" quite a bit. The surface of Mars has craters like Earth's moon and volcanoes, valleys, and polar ice caps like Earth.
Mars has two moons, Phobos and Deimos, but they have not been included in the model because at this scale, Phobos is only a couple hairs' breadths in width and Deimos is even smaller. If you want, you can imagine a tiny speck orbiting about 3 inches above the surface of the model of Mars and an even tinier speck oribiting about 7 inches from the surface.