A Plek-rath ("Visionary Mirror") was a psionic device of Vulcan design.
These were noted as one of the rarest of the psionic technology that was still being manufactured on Vulcan. The creation of these devices were known only to an isolated sect of monks that lived in the mountains near the Fire Plains of Raal. They allowed a user to see a detailed image of any palce they had visisted and knew well or allow them to see any person they had ever mind melded with in the past.
In order to make use of a plek-rath, the user had to percieve the image and meditate on it whereupon they entered a light trance while holding or gazing into the mirror. After 10 to 15 minutes of uninterrupted meditation, the images began to appear in the user's mind. These visionary mirrors were only capable of being used on people or palces on the planet on which their user was based on as the device did not have the power to observe places or individuals that were further away.
Construction of these psionic devices took up to six months to create and were only given to individuals that the monks had deemed truly trustworthy. Typically, the monks required that anyone that sought these devices recite all their important deeds and give a detailed reason for needing these devices. A traditional acceptable reason for awarding these visionary mirrors was either averting a war, resolving a logical contradiction that only the plek-rath can solve or locating the bearer of a relative's Katra. In addition to these requirements, the monks also asked the user to perform some sort of service for their monastery. (Last Unicorn RPG module: The Way of Kolinahr: The Vulcans)