La Cuevona, Natural cave tunnel in Ribadesella, Spain.

La Cuevona is a natural karst tunnel over 300 metres long in the parish of Junco, Ribadesella. A paved road runs through it, and the stream that originally formed the cave flows parallel along one side. Inside, the limestone keeps vaults, hollows, stalactites, stalagmites, columns and flowstone, some named "the Devil's Tongue" and "Santiago's Beards".

The cave originally served as a natural pathway for people traveling to Cuevas del Agua village, before later being developed for modern traffic. Over time, a simple footpath evolved into a proper road that accommodated vehicles, reshaping how the area functioned.

The site is experienced by locals and visitors as a natural wonder where geology becomes part of everyday life. People pass through it regularly for transportation, giving it a functional role that sets it apart from typical tourist caves.

La Cuevona lies about 7 km from Ribadesella; from the town cross the Sella bridge, turn left, pass La Huertona and Sardalla, and follow the signposted turn-off. There is no direct exit from the A-8 motorway, so the cave is reached only from the town centre. The asphalted road through the tunnel is open to both cars and pedestrians, and the interior is lit.

School groups visit La Cuevona to measure how light, temperature and humidity change with distance from the entrance, and to watch how living things shift as the light fades. Blind salamanders, frogs and bats still live inside, though the bats are few and no longer form the large colonies they once did; many moved to nearby Cueva Rosa.