This ramification is the longest of the cave: we have here 3 kilometres of passages. The main ramification extends south-west, to reach the active part of the cave. These are a series of underground lakes, the last of which is a Siphon, a technical term for a system of joint sinkholes. One of the sinkholes has a flowing river, which is the source of water for the lakes. A professional underwater exploration have reached a depth of 80 meters, without still touching the bottom. Another branch, developing north, is a system of galleries, which can be filled completely if torrential rain falls, making the explorations at times difficult. We have to remember that we are in the active part of the cave. This huge amount of water coming from the underground sources are the reason for the rounded vault preceding the entrance. Over the ramification, with only the river flow passing through, the ceiling changes is shape again to show a sharp top.
With Su Stampu e Pireddu are associated, on a local scale, a few legends about the name Pireddu. The best one tells the story of an outlaw, a bandit whose, after committing a few crimes, would hide in this cave. To make is name even more legendary, he would use these underground passages to escape: passing through underground lakes using a boat, he was able to reach Iglesias using these underground tunnels. Obviously professional exploration did not confirm these stories. It is more likely that Pireddu was a local bandit who was sentenced to death and thrown down this part of the cave.