This page contains information regarding Star Trek: Discovery, and thus may contain spoilers.
According to The Story of the Promise, after promising he would return, Kahless pointed to a star, saying, "Look for me there, on that point of light." Boreth circled this star, and the most devout Followers of Kahless awaited his return there. (TNG: "Rightful Heir"; DIS: "Point of Light")
The monastery at Borath contained clerics, high clerics, and monks, as well as guardians. During the 23rd century, it was said that no one left the monestary, and no one who did not belong there ever got in. (TNG: "Rightful Heir";DS9: "The Way of the Warrior";DIS: "Point of Light")
In 2257, A Section 31 ship delivered a baby of the Chancellor of the Klingon High Council L'Rell with Voq to the planet. Considering it a vulnerability, the Chancellor initially hoped to keep the child a secret from her enemies within the High Council. However, following an attempt on the boy's life, she proclaimed that the child had been murdered and sent it to be raised on Boreth as a monk. (DIS: "Point of Light")
In 2369, the high clerics of Boreth produced a clone of Kahless and orchestrated his apparent return from Sto-vo-kor. Worf was present at the monastery when this happened. The nature of the clone was eventually revealed. (TNG: "Rightful Heir")
Following the destruction of the USS Enterprise-D, Worf took extended leave from Starfleet to visit Boreth again. He found his discussions with the clerics there to be there most enlightening. As his leave neared its end, he was pulled back from his studies due to the Federation-Klingon War, but he hoped to return afterwards, even considering resigning from Starfleet. Eventually, Worf remained in Starfleet. (DS9: "The Way of the Warrior")
Background information Edit
In "Rightful Heir", the Boreth landscape and monastery was a matte painting created by Dan Curry. He was inspired by similar structures he had seen in the Himalayas. (Star Trek Encyclopedia (4th ed., vol. 1, p. 93); Star Trek: The Next Generation Companion)
Dialogue from "Rightful Heir" suggests that the monastery was about twelve days by shuttle from the general region in which the Alwanir Nebula was located, and a day's travel from the Klingon homeworld using the USS Enterprise-D. It might also be near the Gariman sector.
There was disagreement on the pronunciation of this planet. Here are the three possible pronunciations:
- "Rightful Heir" pronunciation guide: "BOR-reth" 
- "The Way of the Warrior" pronunciation guide: "BOR-eth" 
- StarTrek.com: "bore-OTH" 
According to Star Trek: Star Charts (p. 62) and Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), Boreth was located in the Boreth system. The system's primary was an M-class star.
The novelization of "The Way of the Warrior" had several scenes set on Boreth.
The Bajoran Ascendancy, from a horrific alternate future in the Star Trek: Deep Space Nine - Millennium trilogy, named a Klingon warship after the planet.
Taking place in 2409, Boreth is also featured in the video game Star Trek Online. Alongside the clone of Kahless, the player has to fight demonic forces of the Fek'Ihri in the lava caves of the planet.