Caves of No'Mat
From Memory Alpha, the free Star Trek reference
The Caves of No'Mat are lava caves located on the planet Qo'noS.
Prolonged exposure to the heat and vapors of these caves together with deep meditation is known to induce hallucinations to Klingons during the Rite of MajQa. When Worf was young, he visited the Caves of No'Mat and had a vision of Kahless. (TNG: "Birthright, Part I", "Rightful Heir")
