The secret sea is made up of seven smaller seas located within subterranean caverns beneath Deltora. These are the Topaz sea, Ruby sea, Opal sea, Lapis Lazuli sea, Emerald sea, Amethyst sea and Diamond sea, though the Lapis Lazuli, Amethyst, and Diamond seas are not known to have ever been explored.
Surrounding these seas is a grey cavern roof that is beneath Deltora'a shores and the Barrier Mountains, while another sea is found beneath the Shadowlands that is black. It's possible that Deltora's other underground borders were also surrounded by black seas.
Beneath the Ruby, Opal, and Emerald seas are the islands colonised by the three Pirran tribes.
Any individual who travels in the secret seas will typically instantly forget their experiences there once they emerge on the surface. There have been a handful of exceptions: Lief, Barda and Jasmine, when they were accompanied by Emlis to the Shadowlands and had the thoughts of all Pirrans focused on them, and the Seven Traitors. Lief, Barda, Jasmine and Doran the Dragonlover were also able to remember the secret sea and the Pirrans after they recieved their Soul-stones.