The Pirran Caverns are a giant underground cave system, running the entire length of Deltora. The Caverns consists of three isles were the three different groups of Pirra settled down, after they were forced out of Pirra by the Shadow Lord. The Caverns are filled with water, forming an underground sea, with the ceiling changing colour to reflect the gemstone of the tribe territory it is situated beneath.
Each Isle's people had a piece of the Pirran Pipe which was split due to trickery by the Shadow Lord. The Plumes had the mouthpiece of the flute, although it was stolen and eventually ended up with Glock. The Auron's had the middle stem, and the Keras had the endpiece.
The barren island is a tiny island located in the Opal caverns, which is also home to the island of Auron and the abandoned Auron rafts. It is apparently without the plant life or fungus seen on the Pirran islands, and its sole inhabitants are a species of large, carnivorous grubs that feed upon sea moles who end up on the island or any travellers unaware of the danger. The island is surrounded by brightly coloured seaweed planted by the Aurons as a warning against danger.
The Auron rafts were built by the Aurons who were exiled from their island when they refused to accept the illusory recreation of Pirra created by many of their fellows. Using materials from the island, they built the rafts, which served as their home for many centuries and were visited by Doran the Dragonlover. After the last of the islanders died and they were able to reclaim the island, it is unknown what became of the rafts; since they were no longer needed it seems likely that the Aurons would have disassembled them to put the material to other uses.
It was believed by Barda that the caverns were beyond the borders of Deltora, hence he suggested that the powers of the Belt of Deltora did not function. Though, Jasmine argued that since the gems came from the earth, the Belt should have been more powerful. Later it was revealed that Belt of Deltora that Lief wore in the caverns was a forgery and the real one was kept on the surface with Marilen.