UTD Spain Fuentona de Muriel 2021 Project

The Area

The Fuentona de Muriel surgency is enclosed in a Natural Reserve in the province of Soria within the autonomous community of Castille y León in Spain. Access to this protected area is highly regulated with special permits required to access the cave.

This cave is “famous” as it was featured in the TV series Al Filo de lo Imposible (On the edge of the impossible) in the early 2000’s.

Fuentona de Muriel Cave

The cave is a surgency for a medium flow river which flows through a limestone canyon it has cut through. After heavy rains in the winter, the cave is known to have very strong flow as the surrounding valleys direct the water straight into this aquifer.

The parking lot is located at about 800m via a well-maintained path which complicates logistical matters. Despite this, using some gear carts it typically takes only about 2 to three trips to get the gear transferred. Direct access to the cave entrance can be done exceptionally via 4×4 with special permits and help from the park rangers.

At the entrance, there is a large pool which provides an easy entrance to the divers.

Upon entering, divers are met with large boulders and the cave tube turns to the right and down into a bigger chamber tube. The cave bifurcates at 50m from the entrance into an upper passage to the left and the lower passage straight on. A third passage exists but the risk of boulders crumbling forbids it’s use.

Both passages reconnect at about -40m and continue in a single passage down to -54m. The passage then becomes a quasi-vertical passage up into the air chamber which climbs inside the mountain in excess of 80m with several streams flowing through it. Deep in this chamber the cave continues with the second submerged section currently explored down to about -100m.

The Project

The project’s objective is to create a high-resolution 3D topography of the first section of the cave using several methods, photogrammetry being the principal method of choice.

Because the cave is large, and it quickly dips several dives and unified dive teams will be required.


The Team

Alan Weinberg (Project co-director & Exploration Diver)

Juan Alberto Achica (Project co-director & Exploration Diver)

Juan Carlos Albert (Exploration Diver)

Iñaki de Santos (Exploration Diver)

Álvaro López (Exploration Diver)

Juan Alfonso Sánchez (Exploration Diver)



The exploration teams have performed several dives to start recoding video for 3D photogrammetry. The large number of boulders present makes this task particularly complicated. Basic line maintenance activities were performed and 3D distance to exit arrows were placed throughout the current line installation all the way to the air cave at about 200m from entry. In addition, exploration of the aerial cave was performed by those certified to dive to at least -54m.

The aerial cave is vast, and transit is very complicated as large boulders about the size of a car or small bus have fallen constraining access to the climb. From that point, access to the second sump was found requiring some climbing gear to descend.

Further dives will be required to install proper safety lines as needed to allow the support team to safely be able to move within the cave when a push is done in the second sump.