Castle of San Martín de Valvení Monument · San Martín de Valvení, Campiña del Pisuerga, Valladolid The remains of the fortress dominate a municipal district of 58.66 square kilometres at 760 metres of altitude. In 1850 the place gathered ninety houses and seventy-seven households that lived on cereal, livestock and charcoal burning. Photo: Lourdes Cardenal (CC BY-SA 4.0) What to see and do in San Martín de Valvení