This old water mill, also known as Molino de Ruiz or Molino de la Grieta was used for grinding cereals to make gofio flour. The mill stands on the left side of the Ruiz ravine, inside the municipality of San Juan de la Rambla, in an area surrounded by prickly pears, which are locally known as "pencas", hence the name of the mill. The mill ran up until 1942 and in 2007 it was declared an Asset of Cultural Interest in the Ethnological Site category. It is comprised of two rectangular buildings with walls made of red-coloured tuff and masonry. Beneath the main building is a chamber where the mill machines used to be, and the mechanism that can still be seen to this day is in incredibly good condition.