Cañon del Pato! 35 tunnels in about 13 km, all dirt. It was not as pretty as what we'd been expecting, but very pleasant, and we didn't meet any vehicles in tunnels, although we could have. If you come this way, you must have a light. The tunnels are not too long, but they are narrow.

13 km of dirt, followed by mostly pavement. Mostly gentle climbing.