The largest of the cavities known by this name has its entrance among blocks and descends gently to the start of a slightly descending gallery with some connections to the outside through the ceiling side. Structured according to an orthogonal network of fractures, with numerous clastic products that give it a rugged route, in which one must scramble down from block to block.

The lithological materials in which the Balmes d'en Caxurma are located are somewhat complicated. According to the map of the Institut Geològic they are marls with lutites, and according to the ICC geological map they would be sandstones; in any case, both agree that they are from the Lutetian. In principle we lean more toward the second option.

Advancing, one quickly finds a first fork; continuing to the right, the entrance gallery continues among blocks until it becomes totally impenetrable; shortly before this end and through a small hole on the left, one enters a narrow gallery with a rugged route over small steps and descending and ascending ramps. Along this gallery there are, both to the right and to the left, different conduits just over 10 metres long at the longest. After a small step and right beside it, on the left according to the direction of travel, a series of small galleries begins which, like the one a few metres further on, lead to the parallel gallery that we will discuss next. From this last fork and continuing forward, by a short ascending ramp one can exit to the outside through the northernmost opening of the cavity.

Returning to the second fork, now to the right, one reaches a gallery parallel to the entrance one, with a higher ceiling and an ascending route among blocks. Soon on the left one finds the other conduit that leads to the previous gallery; further on the ceiling lowers considerably, then rises again immediately and continues thus for a few more metres, where by an ascending step of about 2 metres one reaches the entrance vestibule.

Given the apparently labyrinthine structure of the cavity, cords and various markings, not always discreet, are found, aimed at finding the right way. In one of the small chambers there is a wall with multiple inscriptions and engravings, among which some centuries-old ones can be distinguished.