I think you mean hairpin bends, but yes, the idea has been discussed many times. You will find several topics already exist here about this. Many people would like the addition of mountainous terrain.
Would the Bonneville Salt Flats (or any World Speed Record type locale) count? That's in a valley. It has also been suggested
I'd still like to see a two-lane wide tarmac rally type stage. Something really fast and decently challenging, with massive elevation changes and some innovative features no normal race course has. (Realistic, though, naturally.) Whether or not it's on a mountain side is of no importance; although I think it would make the most sense geographically for it to be on a mountain :P