This site has been explored and surveyed by the Grupo Espeleológico de Santander del C.A. Tajahierro. Their survey is published in Exploraciones en Solorzano (Santander) in Los Sótanos de la Tierra, No. 5, 1980, Santander (ref. 1980a). Unfortunately the entrance position (along with many others in the publication) is very unreliable although attempts have been made to alter the given Madrid grid reference through a Greenwich grid reference to an ETRS89 grid reference, seen above.
The site, named by los lugareños, has not yet been located but it is apparently in the same area as site 4004.

Reference: anon., 1980a; anon., 2014b (Easter logbook)
Entrance picture :
Underground pictures :
Video :
Detailed survey : from anon., 1980a
Line Survey :
On area survey :
Survex file :