The knowledge of the Ancients from the repository on P3X-439 led SG-1 to the planet Praclarush Taonas. The name translates as "Lost in Fire", and the pronunciation of its name corresponds to the stargate glyphs of its gate address when spoken aloud: 35-3-31-29-5-17. Once home to one of the earliest Lantian cities, Praclarush Taonas had been abandoned when the inhabitants learned that their sun was nearing the end of its life.
The planet is within our galaxy, and SG-1 traveled there by cargo ship, hoping to find the Lost City of the Ancients. However, they found instead a world truly lost in fire, covered by lava flows, and orbiting a star that had become a red giant. A small dome-shaped anomaly on the surface was the remains of an Ancient outpost, once protected by a now-inactive force field, and perhaps dating back millions of years to a time when the planet flourished.
Within the outpost, SG-1 discovered a throne-like chair of Ancient design which activated when O'Neill sat in it, and which displayed a holographic map of the galaxy. The image of Earth did not take into consideration 30 million years of continental drift, but O'Neill indicated, "Terra Atlantus," that the key to the Lost City of Atlantis lay beneath the ice of Antarctica. SG-1 also retrieved the chair's crystal power source, a zero point module, or ZPM, and returned with it to Earth as the integrity of the dome structure weakened and the Ancient outpost collapsed and was lost once more.
Episode Reference: Lost City
Stargate Coordinates: 35-3-31-29-5-17