In the history of this cavity, urban legends intertwine with part of reality. Having family ties in Camarasa allowed me during the sixties and seventies of the last century to spend some time there and to have the opportunity to talk with the elderly people who had taken part both in the construction of the Camarasa dam and in the excavation of tunnel 3 of Coll de Porte and who were still alive.

As for the tunnel built in the mid-twenties of the last century, it has the particularity that during its excavation a large cavity was found inside. In order to bypass it, part of the tunnel was built supported by a 70-metre-long viaduct. This viaduct consists of four spans of 10 metres each, supported on double piers. The design makes use of the tunnel's shape so that the tunnel's side walls form two continuous beams on which the deck rests. The elderly people told me that more than seven train wagons loaded with cement were needed to build the viaduct. Furthermore, during the excavation of the tunnel at this point a spring of water appeared, which made them stop the excavation for almost a month until no more water came out; as a result, they said, part of the mountain above collapsed. In the 1945 ICGC aerial photographs it can be seen that the hole was already there.

Taking into account that the terrain is gypsum, the relationship between both phenomena cannot be ruled out.