AB-4

The entrance of the pit opens at the bottom of a large doline. The cavity begins with a 7-metre shaft that leads into a small chamber and continues along a descending ramp. From the 5-metre shaft onwards the cavity increases notably in size, leading into a 14-metre shaft after which a 10-metre shaft-ramp and an 8-metre one follow in succession. After a ledge one reaches a large 38-metre shaft (the block shaft), after which one emerges into a meander with two branches that soon join. The meander gradually becomes narrower until it becomes impenetrable.

At the bottom of this uncomfortable meander a small inflow of water runs along its floor. At the end of the meander a small air circulation becomes apparent.

From the descending ramp one can take a path that, after a 90º turn, leads into a gallery that goes nowhere, or else take on the right a fossil gallery of modest dimensions, very unstable and deteriorated, with blocks fallen from its ceiling. Subsequently one reaches a 5-metre shaft.