Peña Blanca is a white-and-red rock formation on the edge of Humahuaca, reached by a short walk from town. A small shrine is built into the rock, and steps lead up to a viewpoint over the valley and the dry, folded hills around it.
It is not a long excursion, but it is a good leg-stretching walk if you have already seen the town centre. Go in the cooler part of the day; the route is exposed and the light is better early or late.