I've created a little stone bridge from tiles. Again, the bridge is made from two layers of tiles, creating a 'foreground' and 'background' element allowing the cyclist to appear to be riding between those layers. The system that I use to define a path for the cyclists allows me to easily add the hump for the bridge. It looks great when the peloton rides over it.
I might experiment with using rivers or waterfalls as natural breaks in the scenery. This might get around the problem of how to blend urban to rural and make it look convincing.
