The longuest I remember and modestly photographed is the 84 miles between Mount Aigoual and Mount Ventoux, France. You have to plan it on a beautiful day after a rainy one.
Not being in tattoos and thus not knowing anything, I've always wondered what would become of them with the inevitable weight gain, skin aging, or, like a distant cousin, the effects of pregnancy on that huge tattoo she has all along her ribs...