The Julih Tunnel is a secret passageway located in the Namornese Imperial Palace in Dancruan and opens onto the treacherous lake known as the Syth. The tunnel is kept extremely secret, but the Mages' Society of Namorn has access to the plans. It saved Berenene dor Ocmore from multiple assassination attempts.
It was easily destroyed by Trisana Chandler using weather magic. She warned Ishabal Ladyhammer and Quenaill Shieldsman not to stop her when they looked like they planned to, because she cited disastrous results if they did. This, among with quite a few other displays of Tris's magic, convinced Empress Berenene that Tris was the most dangerous one of the four, underestimating the others, especially Sandry.