I think prairies offer the third-best view of the sky, out of any terrain type. The best for seeing the sky (and horizon) would be up a mountaintop, and the second best would be the ocean. Huge skies of 180 degrees! Or more, if you have elevation.
Myself, I live in a fairly bumpy place... British Columbia, Canada. We have to go East to Alberta if we want truly flat prairies :P