Go early, as there's very little shade along the way and the sun makes for hot afternoons throughout much of the year. I encountered a few packs of dogs, none of which proved hostile, but it was a bit unnerving. Perhaps walking sticks or some dog treats in hand might give you a little piece of mind. There are some great restaurants in Santa Rosa de Lima at the end of the ride. And an easy, cheap bus can whisk you back to Guanajuato should you choose not to make the round trip back.