The caves of Matienzo have been visited since prehistoric times, and the oldest evidence which has been found dates back to Magdalenian times. Nevertheless, nowhere within Matienzo has there been found a site used as a habitat over a long period of time. But Cueva de los Emboscados and Cueva del Patatal have engravings and a painting, although in neither cases are these too far from the entrance. The bone-arrow point at the end of the Pintó Gallery in Risco would have been taken in through a former entrance, now collapsed, and the stone wall at the end of Cueva del Agua must have been built when an entrance was open there. So we can hardly talk of cave exploration at that time in Matienzo (unlike, for example, in Ramales de la Victoria, with cave paintings over a kilometre inside Cueva Cullalvera). By the Chalcolithic or Bronze Ages some entrances were being used for human burials; Cueva de Rascavieja is one example.
In the Iron Age several caves were used for burials, rituals, or storage; Cueva de Cofresnedo is the most spectacular case. And here, as pottery has been found about 300m from the entrance, in an obscure alcove at the top of a 2m climb, we can say that the population of the last centuries BC really were exploring caves.
Pottery from the Medieval period has also been found in several caves, especially Cueva Cuatribú, where the jug was apparently associated with a hearth.
The word "Carcavuezo" is used by the poet and novelist Francisco Quevedo in the early 17th century; as he was associated with Santander, it's possible that he visited Matienzo.
The first written record of the caves dates from 1848, in the Madoz dictionary. This says the river of Matienzo rises at Comellantes, crosses the valley and then goes under a mountain, resurges and sinks again in La Secada, to reappear in Secadura (this was nearly 120 years before the first known dye-test).It also mentions the periodic flooding. However there is no description of the caves internally.
In the 19th Century, with the new interest in Geology and Natural History, we can expect that the caves of Matienzo received visits. But there is little evidence for this, and the descriptions in Puig y Larraz's catalogue of Spanish caves (1894) are fairly poor. Comellantes, the source of the river, is said to be not very large. The sink at Agua (called Pozo de Guzmartín) is described as having a steeply descending floor, and the resurgence is called Cobadal de Matienzo. Carcavuezo is called Pozo Nuevo, while there is a mention of several "Cuevas de La Secada", of differing sizes, which act as floodwater sinks. Finally there is Pozo de Mullir, a pothole located in the centre of the depression with an area of 500 square metres to the North of Mullir and the South-west of the Aras valley (Hoyo de Llusa). At the turn of the century caves in Ramales de la Victoria and even Ogarrio (Cueva de Llusa) were visited by archaeologists, but again we have no records that any prospecting was carried out in Matienzo.
Many of the caves have, of course, been visited and used by the inhabitants of Matienzo, but once more this hardly counts as exploration.
Goats and sheep are kept in some of the larger entrances, such as Cuatribú; while Cueva de Germán was equipped as a cowshed. Some caves, like Cubio de la Reñada, were used as cold stores for butter, while others, such as Cueva del Pico del Hayal (Llueva), have pools which were a source of water for the farmers working near the cave. Goat excrement was dug from some entrances to be used as fertilizer (eg Cueva del Abono). Many pots have been descended to rescue fallen animals; the most spectacular descent almost certainly being Alpine Chough Pot (-70m). Certain caves were chosen for visits by children, and hundreds of their names can be seen on the walls of Cueva de las Cosas. There is also the story of a madwoman called Ramona who lived in a cave (now called Cueva de la Loca) for about a week, and traversed it - presumably without a light - to re-emerge from a second entrance, since collapsed and covered over. Following the fall of Santander to the Francoist forces in the Civil War a number of local men had to hide in the caves, particularly in La Vega and on Mullir. Cueva de la Calleja Rebollo has large mounds of rubbish left behind by these "maquis".
Caving really took off in Cantabria in the late 1950s with the arrival of cavers from Dijón (France) in the Asón valley. But it seems that the nearest they got to Matienzo was Sima del Cueto, on the ridge between Matienzo and Bustablado. In August 1959 they descended this massive hole; a 110m ladder climb, followed by a boulder slope reaching the base 40m lower.
Also in the 50s the Provincial authorities (Diputación de Santander) trained a team of workmen to explore the caves of the region. These men, whose normal job was to repair the roads and cut the grass at the sides, were given the task of searching for archaeological remains. It's known that they visited Matienzo, and such caves as Patatal, Coburruyo and Peña Cubillones, but they left no written record of their work.
The sport had its beginnings in Matienzo in the early 1960s. Groups of boys spending their long summer holidays in the village had no means of transport for moving around and had to find ways of amusing themselves in Matienzo itself. This, as always, included visiting caves such as Cofresnedo, Cosas, Tiva or Agua. Lights were no problem as it was still common for acetylene lamps to be used as a form of domestic lighting, and carbide could be bought locally. What made these visits different now was that among these boys was Juan Carlos Fernández Gutiérrez, a student of Geology in Madrid, with a real interest in caving. He acquired a caving ladder, and this was put to use in Cueva Coquisera. And when the other boys got tired of going to the same caves, Juan Carlos would set off alone, sometimes causing his family to worry when he was late in returning.