It just came to my mind seeing friends riding from Tucson.
There is a great loop in Saguaro park… sure a few here know it:
Not easy, but would it be great if the user base could help creating new terrain/courses to ride on?
Take a actual ride (GPS / GPX data), (auto) create a road from that with some parameters like # lanes, etc…
Fetch elevation data online to model terrain around the road
Then have some basic decoration elements (trees, cacti, buildings, …) to make it nice.